Fix the bundled Paho C build foc C23 compilers by forcing C99 compliance in CMake build

Author: fpagliughi

CMakeLists.txt

@@ -71,6 +71,7 @@ if(PAHO_WITH_MQTT_C)
     if(NOT WIN32)
         set(PAHO_WITH_UNIX_SOCKETS TRUE CACHE BOOL "Support for Unix-domain sockets")
     endif()
+    set(CMAKE_C_STANDARD 99 CACHE STRING "Paho C language standard")
 
     add_subdirectory(${PROJECT_SOURCE_DIR}/externals/paho-mqtt-c)