Fix compilation with MinGW versions without threads support

Older versions of MinGW don't provide std::mutex or std::thread

.gitmodules

@@ -28,3 +28,6 @@
 [submodule "src/3rdparty/weakjack/weakjack"]
 	path = src/3rdparty/weakjack/weakjack
 	url = https://github.com/x42/weakjack.git
+[submodule "src/3rdparty/mingw-std-threads"]
+	path = src/3rdparty/mingw-std-threads
+	url = https://github.com/meganz/mingw-std-threads.git

cmake/build_win32.sh

@@ -37,4 +37,4 @@ fi
 CMAKE_OPTS="-DCMAKE_PREFIX_PATH=$MINGW $CMAKE_OPTS"
 
 # shellcheck disable=SC2086
-cmake "$DIR/.." -DCMAKE_TOOLCHAIN_FILE="$TOOLCHAIN" -DCMAKE_MODULE_PATH="$DIR/../cmake/modules/" $CMAKE_OPTS
+cmake "$DIR/.." -DCMAKE_TOOLCHAIN_FILE="$TOOLCHAIN" $CMAKE_OPTS

plugins/vst_base/RemoteVstPlugin.cpp

@@ -59,7 +59,12 @@
 #define USE_WS_PREFIX
 #include <windows.h>
 
-#include <mutex>
+#ifdef USE_MINGW_THREADS_REPLACEMENT
+#	include <mingw.mutex.h>
+#else
+#	include <mutex>
+#endif
+
 #include <vector>
 #include <queue>
 #include <string>

plugins/vst_base/RemoteVstPlugin/CMakeLists.txt

@@ -4,9 +4,11 @@ project(RemoteVstPlugin
 set(CMAKE_CXX_STANDARD 11)
 
 include(CheckCXXPreprocessor)
+include(CheckCXXSourceCompiles)
 
 CHECK_CXX_DEFINE(IS_WIN "_WIN32")
 CHECK_CXX_DEFINE(IS_WIN64 "_WIN64")
+CHECK_CXX_DEFINE(IS_MINGW "__MINGW32__")
 
 if(NOT IS_WIN)
 	message(FATAL_ERROR "Toolchain used does not target windows.")
@@ -35,6 +37,25 @@ if(WIN32)
 	target_link_libraries(${EXE_NAME} Qt5::Core)
 endif()
 
+if(IS_MINGW)
+	SET(CMAKE_REQUIRED_FLAGS "-std=c++11")
+
+	CHECK_CXX_SOURCE_COMPILES("
+	#include <mutex>
+	int main(int argc, const char* argv[]) {
+		std::mutex m;
+		return 0;
+	}
+	" HAS_STD_MUTEX)
+
+	if(NOT HAS_STD_MUTEX)
+		target_include_directories(${EXE_NAME} PRIVATE
+			"${CMAKE_SOURCE_DIR}/src/3rdparty/mingw-std-threads")
+		target_compile_definitions(${EXE_NAME} PRIVATE
+			-DUSE_MINGW_THREADS_REPLACEMENT)
+	endif()
+endif()
+
 IF(STRIP)
 	ADD_CUSTOM_COMMAND(TARGET RemoteVstPlugin32 POST_BUILD COMMAND "${STRIP}" "$<TARGET_FILE:RemoteVstPlugin32>")
 ENDIF()