Let cmake find out if threads.h is available

CMakeLists.txt

@@ -50,6 +50,7 @@ add_custom_target(clap-tests)
 
 if (${CLAP_BUILD_TESTS})
     message(STATUS "Including CLAP tests, compile tests, and versions")
+    include(CheckIncludeFile)
 
     macro(clap_compile_cpp SUFFIX EXT STDC STDCPP)
         add_executable(clap-compile-${SUFFIX} EXCLUDE_FROM_ALL src/main.${EXT})
@@ -84,11 +85,17 @@ if (${CLAP_BUILD_TESTS})
     clap_compile_cpp(cpp17 cc 17 17)
     clap_compile_cpp(cpp20 cc 17 20)
 
+    check_include_file(threads.h CLAP_HAS_THREADS_H)
+
     add_library(clap-plugin-template MODULE EXCLUDE_FROM_ALL src/plugin-template.c)
     target_link_libraries(clap-plugin-template PRIVATE clap)
     set_target_properties(clap-plugin-template PROPERTIES C_STANDARD 11)
     add_dependencies(clap-tests clap-plugin-template)
 
+    if(CLAP_HAS_THREADS_H)
+        target_compile_definitions(clap-plugin-template PRIVATE CLAP_HAS_THREADS_H)
+    endif()
+
     if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
         target_link_libraries(clap-plugin-template PRIVATE -Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/src/linux-my_plug.version)
         target_link_libraries(clap-plugin-template PRIVATE -Wl,-z,defs)

src/plugin-template.c

@@ -8,7 +8,7 @@
 #include <stdio.h>
 #include <assert.h>
 
-#if __STDC_VERSION__ >= 201112L && !defined(__STDC_NO_THREADS__) && !defined(_MSC_VER)
+#if __STDC_VERSION__ >= 201112L && !defined (__STDC_NO_THREADS__) && defined (CLAP_HAS_THREADS_H)
 #   define CLAP_HAS_THREAD
 #   include <threads.h>
 #endif