Disable MinGW std threads includes by default

In preparation for removal later

CMakeLists.txt

@@ -282,7 +282,7 @@ endif()
 set_target_properties(openttd PROPERTIES OUTPUT_NAME "${BINARY_NAME}")
 # All other files are added via target_sources()
 
-if (MINGW)
+if (MINGW AND OPTION_MINGW_STDTHREADS)
     target_link_libraries(${OPENTTD_LIB} mingw_stdthreads)
 endif()
 

src/3rdparty/CMakeLists.txt

@@ -6,7 +6,10 @@ add_subdirectory(squirrel)
 add_subdirectory(nlohmann)
 add_subdirectory(opengl)
 add_subdirectory(cpp-btree)
-add_subdirectory(mingw-std-threads)
 add_subdirectory(monocypher)
 add_subdirectory(randombytes)
 add_subdirectory(robin_hood)
+
+if (MINGW AND OPTION_MINGW_STDTHREADS)
+	add_subdirectory(mingw-std-threads)
+endif()