CMake !@#$%^&*()*&^5 sh*te fixes and tweaks:

- https://gitlab.kitware.com/cmake/cmake/-/issues/21476

Work-around for that does not fly without:
https://stackoverflow.com/questions/11801186/cmake-unable-to-determine-linker-language-with-c/11802004#answer-11802004
as you'ld otherwise end up with missing default libs for the linker in MSVC in CXX/C++ mode.

And, NO, https://stackoverflow.com/questions/56462415/cmake-error-cannot-determine-link-language-for-target (`set_target_properties($target PROPERTIES LINKER_LANGUAGE CXX)`) does NOT suffice!

Author: GerHobbelt

.gitignore

@@ -232,6 +232,7 @@ $RECYCLE.BIN/
 *.egg-info
 dist/
 build/
+b/
 eggs/
 parts/
 var/
@@ -272,4 +273,4 @@ pip-log.txt
 /windows/VS2019/Release-*/
 
 .idea
-cmake-build*
+cmake-build*

CMakeLists.txt

@@ -13,7 +13,7 @@ message(STATUS "Generator ......... ${CMAKE_GENERATOR}")
 message(STATUS "Build Type ........ ${CMAKE_BUILD_TYPE}")
 message(STATUS "Version ........... ${PTHREADS4W_VERSION}")
 
-project(pthreads4w VERSION ${PTHREADS4W_VERSION} LANGUAGES C)
+project(pthreads4w VERSION ${PTHREADS4W_VERSION} LANGUAGES C CXX)
 
 set(PTW32_VER ${PROJECT_VERSION_MAJOR}${EXTRAVERSION})
 if(NOT CMAKE_DEBUG_POSTFIX)
@@ -91,9 +91,9 @@ if(MSVC)
     # (Note: If you are using Microsoft VC++6.0, the library needs to be built
     # with /EHa instead of /EHs or else cancellation won't work properly.)
     if(MSVC_VERSION EQUAL 1200)
-        set(VCEFLAGS  "/EHa /TP ")
+        set(VCEFLAGS  "/EHa ")
     else()
-        set(VCEFLAGS  "/EHs /TP ")
+        set(VCEFLAGS  "/EHs ")
     endif()
 
     add_definitions(-DHAVE_CONFIG_H -DPTW32_RC_MSC)
@@ -113,10 +113,15 @@ endif()
 
 macro(shared_lib type def)
     set(targ pthread${type}${PTW32_VER})
-    add_library(${targ} SHARED pthread.c ${CMAKE_CURRENT_BINARY_DIR}/version.rc)
+    if(${type} STREQUAL "VCE" OR ${type} STREQUAL "VSE")
+		add_library(${targ} SHARED pthread-EH.cpp ${CMAKE_CURRENT_BINARY_DIR}/version.rc)
+		#set_target_properties(${targ} PROPERTIES LINKER_LANGUAGE CXX)
+	else()
+	    add_library(${targ} SHARED pthread-JMP.c ${CMAKE_CURRENT_BINARY_DIR}/version.rc)
+	endif()
     message(STATUS ${targ})
     target_compile_definitions(${targ} PUBLIC "-D${def}")
-    if(${type} STREQUAL "VCE")
+    if(${type} STREQUAL "VCE" OR ${type} STREQUAL "VSE")
         set_target_properties(${targ} PROPERTIES COMPILE_FLAGS ${VCEFLAGS})
     endif()
     if(${CMAKE_GENERATOR} MATCHES "Visual Studio")
@@ -130,10 +135,15 @@ endmacro()
 
 macro(static_lib type def)
     set(targ libpthread${type}${PTW32_VER})
-    add_library(${targ} STATIC pthread.c)
+    if(${type} STREQUAL "VCE" OR ${type} STREQUAL "VSE")
+		add_library(${targ} STATIC pthread-EH.cpp)
+		#set_target_properties(${targ} PROPERTIES LINKER_LANGUAGE CXX)
+	else()
+	    add_library(${targ} STATIC pthread-JMP.c)
+	endif()
     message(STATUS ${targ})
     target_compile_definitions(${targ} PUBLIC "-D${def}" -DPTW32_STATIC_LIB)
-    if(${type} STREQUAL "VCE")
+    if(${type} STREQUAL "VCE" OR ${type} STREQUAL "VSE")
         set_target_properties(${targ} PROPERTIES COMPILE_FLAGS ${VCEFLAGS})
     endif()
     if(${CMAKE_GENERATOR} MATCHES "Visual Studio")
@@ -143,24 +153,13 @@ macro(static_lib type def)
     endif()
 endmacro()
 
+shared_lib ( VCE PTW32_CLEANUP_CXX )
+shared_lib ( VSE PTW32_CLEANUP_SEH )
+shared_lib ( VC  PTW32_CLEANUP_C )
 
-option(PTHREAD_BUILD_SHARED_LIBRARY "Build shared library" OFF)
-set(_build_shared_library ${PTHREAD_BUILD_SHARED_LIBRARY})
-set(PTHREAD_BUILD_TYPE "VC" CACHE STRING "VC/VSE/VCE")
-
-if(PTHREAD_BUILD_TYPE STREQUAL "VC")
-    set(def_ PTW32_CLEANUP_C)
-elseif(PTHREAD_BUILD_TYPE STREQUAL "VSE" OR PTHREAD_BUILD_TYPE STREQUAL "VCE")
-    set(def_ PTW32_CLEANUP_C)
-else()
-    message(FATAL_ERROR "Unsupported pthread type ${PTHREAD_BUILD_TYPE}")
-endif()
-
-if(_build_shared_library)
-    shared_lib (${PTHREAD_BUILD_TYPE} PTW32_CLEANUP_C)
-else()
-    static_lib (${PTHREAD_BUILD_TYPE} PTW32_CLEANUP_C)
-endif()
+static_lib ( VCE PTW32_CLEANUP_CXX )
+static_lib ( VSE PTW32_CLEANUP_SEH )
+static_lib ( VC  PTW32_CLEANUP_C )
 
 #################################
 # Install                       #

pthread-EH.cpp

@@ -0,0 +1,54 @@
+/*
+ * pthread-EH.cpp
+ *
+ * Description:
+ * Work-around for https://gitlab.kitware.com/cmake/cmake/-/issues/21476 and
+ * other rigs where 'compile C source file as C++' enforcement is a problem.
+ * 
+ * Quoting the CMake issue (remark by Kevin Puetz, 2020):
+ *
+ *     One answer that just came to mind: create a pthread.cxx, that just 
+ *     consists of #include "pthread.c", and let the preprocessor paste the 
+ *     code in. Then CMake just sees two files and it's all normal. [...]
+ *
+ * See also https://discourse.cmake.org/t/compiling-c-as-c-in-cmake-3-18/2172.
+ *
+ * --------------------------------------------------------------------------
+ *
+ *      pthreads-win32 - POSIX Threads Library for Win32
+ *      Copyright(C) 1998 John E. Bossom
+ *      Copyright(C) 1999-2021 pthreads-win32 / pthreads4w contributors
+ *
+ *      Homepage1: http://sourceware.org/pthreads-win32/
+ *      Homepage2: http://sourceforge.net/projects/pthreads4w/
+ *
+ *      The current list of contributors is contained
+ *      in the file CONTRIBUTORS included with the source
+ *      code distribution. The list can also be seen at the
+ *      following World Wide Web location:
+ *      http://sources.redhat.com/pthreads-win32/contributors.html
+ * 
+ *      This library is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU Lesser General Public
+ *      License as published by the Free Software Foundation; either
+ *      version 2 of the License, or (at your option) any later version.
+ * 
+ *      This library is distributed in the hope that it will be useful,
+ *      but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *      Lesser General Public License for more details.
+ * 
+ *      You should have received a copy of the GNU Lesser General Public
+ *      License along with this library in the file COPYING.LIB;
+ *      if not, write to the Free Software Foundation, Inc.,
+ *      59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ *
+ * --------------------------------------------------------------------------
+ */
+
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#define __PTHREAD_JUMBO_BUILD__ 1
+#include "pthread.c"

pthread-JMP.c

@@ -0,0 +1,49 @@
+/*
+ * pthread-JMP.c
+ *
+ * Description:
+ * Addition to the work-around for https://gitlab.kitware.com/cmake/cmake/-/issues/21476 and
+ * other rigs where 'compile C source file as C++' enforcement is a problem.
+ * 
+ * This is the master 'jumbo' C loader file, which will only expand `pthread.c`
+ * contents when those DO NOT require C++ compiler mode.
+ *
+ * --------------------------------------------------------------------------
+ *
+ *      pthreads-win32 - POSIX Threads Library for Win32
+ *      Copyright(C) 1998 John E. Bossom
+ *      Copyright(C) 1999-2021 pthreads-win32 / pthreads4w contributors
+ *
+ *      Homepage1: http://sourceware.org/pthreads-win32/
+ *      Homepage2: http://sourceforge.net/projects/pthreads4w/
+ *
+ *      The current list of contributors is contained
+ *      in the file CONTRIBUTORS included with the source
+ *      code distribution. The list can also be seen at the
+ *      following World Wide Web location:
+ *      http://sources.redhat.com/pthreads-win32/contributors.html
+ * 
+ *      This library is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU Lesser General Public
+ *      License as published by the Free Software Foundation; either
+ *      version 2 of the License, or (at your option) any later version.
+ * 
+ *      This library is distributed in the hope that it will be useful,
+ *      but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *      Lesser General Public License for more details.
+ * 
+ *      You should have received a copy of the GNU Lesser General Public
+ *      License along with this library in the file COPYING.LIB;
+ *      if not, write to the Free Software Foundation, Inc.,
+ *      59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ *
+ * --------------------------------------------------------------------------
+ */
+
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#define __PTHREAD_JUMBO_BUILD__ 1
+#include "pthread.c"

pthread.c

@@ -2,7 +2,7 @@
  * pthread.c
  *
  * Description:
- * This translation unit agregates pthreads-win32 translation units.
+ * This translation unit aggregates pthreads-win32 translation units.
  * It is used for inline optimisation of the library,
  * maximising for speed at the expense of size.
  *
@@ -39,6 +39,9 @@
  * --------------------------------------------------------------------------
  */
 
+// See pthread-EH.cpp and pthread-JMP.c: prevent double definitions in monolithic (automated) builds
+#ifdef __PTHREAD_JUMBO_BUILD__
+
 #ifdef HAVE_CONFIG_H
 # include "config.h"
 #endif
@@ -194,3 +197,5 @@
 #include "pthread_setname_np.c"
 #include "pthread_setspecific.c"
 #include "pthread_getspecific.c"
+
+#endif

pthread.h

@@ -86,7 +86,7 @@
 #else
 # define PTW32_CLEANUP_C
 #endif
-#endif
+#endif // SEH || CXX || C
 
 #if defined( PTW32_CLEANUP_SEH ) && ( !defined( _MSC_VER ) && !defined (PTW32_RC_MSC))
 #error ERROR [__FILE__, line __LINE__]: SEH is not supported for this compiler.