Bug 1407513 Turn std:future back on for ANGLE in the MinGW build now that we have winpthreads r=jgilbert

MozReview-Commit-ID: 9K2Bqtvxemo

--HG--
extra : rebase_source : ab3e9e924734125d94a5460057c6b36f96c4b9a8

gfx/angle/src/libANGLE/features.h

@@ -55,7 +55,7 @@
 // Controls if our threading code uses std::async or falls back to single-threaded operations.
 // TODO(jmadill): Enable on Linux once STL chrono headers are updated.
 #if !defined(ANGLE_STD_ASYNC_WORKERS)
-#if !defined(__MINGW32__) && defined(ANGLE_PLATFORM_WINDOWS)
+#if defined(ANGLE_PLATFORM_WINDOWS)
 #define ANGLE_STD_ASYNC_WORKERS ANGLE_ENABLED
 #else
 #define ANGLE_STD_ASYNC_WORKERS ANGLE_DISABLED