CMake: Fix web export issue godotengine#1830

- cache emscripten variables to make them available in consumers
- add -sUSE_PTHREADS=1 to link flags
- add =1 to sSIDE_MODULE=1 in compile flags to match scons.

Author: enetheru

cmake/emsdkHack.cmake

@@ -25,14 +25,14 @@ Overwrite Shared Library Properties to allow shared libs to be generated.
 ]=======================================================================]
 if(EMSCRIPTEN)
     set_property(GLOBAL PROPERTY TARGET_SUPPORTS_SHARED_LIBS TRUE)
-    set(CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS "-sSIDE_MODULE=1")
-    set(CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS "-sSIDE_MODULE=1")
-    set(CMAKE_SHARED_LIBRARY_SUFFIX) # remove the suffix from the shared lib
-    set(CMAKE_STRIP FALSE) # used by default in pybind11 on .so modules
+    set(CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS "-sSIDE_MODULE=1" CACHE INTERNAL "")
+    set(CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS "-sSIDE_MODULE=1" CACHE INTERNAL "")
+    set(CMAKE_SHARED_LIBRARY_SUFFIX ""  CACHE INTERNAL "") # remove the suffix from the shared lib
+    set(CMAKE_STRIP FALSE ""  CACHE INTERNAL "") # used by default in pybind11 on .so modules
 
     # The Emscripten toolchain sets the default value for EMSCRIPTEN_SYSTEM_PROCESSOR to x86
     # and copies that to CMAKE_SYSTEM_PROCESSOR. We don't want that.
-    set(CMAKE_SYSTEM_PROCESSOR "wasm32")
+    set(CMAKE_SYSTEM_PROCESSOR "wasm32" CACHE INTERNAL "")
     # the above prevents the need for logic like:
     #if( ${CMAKE_SYSTEM_NAME} STREQUAL Emscripten )
     #    set( SYSTEM_ARCH wasm32 )

cmake/web.cmake

@@ -21,7 +21,7 @@ function(web_generate)
     target_compile_options(
         godot-cpp
         PUBLIC #
-            -sSIDE_MODULE
+            -sSIDE_MODULE=1
             -sSUPPORT_LONGJMP=wasm
             $<${THREADS_ENABLED}:-sUSE_PTHREADS=1>
     )
@@ -33,6 +33,7 @@ function(web_generate)
             -sSUPPORT_LONGJMP=wasm
             -fvisibility=hidden
             -shared
+            $<${THREADS_ENABLED}:-sUSE_PTHREADS=1>
     )
 
     common_compiler_flags()