Add pthreads option for emscripten

CMakeLists.txt

@@ -60,6 +60,7 @@ file(TOUCH "${PROJECTM_DUMMY_SOURCE_FILE}")
 
 if(CMAKE_SYSTEM_NAME STREQUAL Emscripten)
     set(ENABLE_EMSCRIPTEN ON CACHE BOOL "Build for web with emscripten. Will also build the SDL2-based entrypoint." FORCE)
+    option(USE_PTHREADS "Enable multithreading support" OFF)
 else()
     set(ENABLE_EMSCRIPTEN OFF CACHE BOOL "Build for web with emscripten. Requires emscripten toolset for building." FORCE)
 endif()
@@ -122,6 +123,11 @@ if(ENABLE_EMSCRIPTEN)
             "SHELL:-s NO_DISABLE_EXCEPTION_CATCHING"
             )
 
+    if(USE_PTHREADS)
+        add_compile_options("SHELL:-s USE_PTHREADS=1")
+        add_link_options("SHELL:-s USE_PTHREADS=1")
+    endif()
+
     set(USE_GLES ON)
 else()
     if(ENABLE_SDL_UI)
@@ -242,6 +248,9 @@ if(ENABLE_SDL_UI)
 endif()
 message(STATUS "    OpenGL ES:               ${ENABLE_GLES}")
 message(STATUS "    Emscripten:              ${ENABLE_EMSCRIPTEN}")
+if(CMAKE_SYSTEM_NAME STREQUAL Emscripten)
+    message(STATUS "    - PThreads:              ${USE_PTHREADS}")
+endif()
 message(STATUS "    Use system GLM:          ${ENABLE_SYSTEM_GLM}")
 message(STATUS "    Link UI with shared lib: ${ENABLE_SHARED_LINKING}")
 message(STATUS "")