CPU lightmapper fixes.

- Fix Embree runtime when using MinGW (patch by @RandomShaper).
- Fix baking of lightmaps on GridMaps.
- Fix some GLSL errors.
- Fix overflow in the number of shader variants (GLES2).

thirdparty/embree/common/tasking/taskschedulerinternal.cpp

@@ -361,7 +361,15 @@ namespace embree
           if ((loopIndex % LOOP_YIELD_THRESHOLD) == 0)
             yield();
           else
+// -- GODOT start --
+#if !defined(__MINGW32__)
+// -- GODOT end --
             _mm_pause();
+// -- GODOT start --
+#else
+            usleep(1);
+#endif
+// -- GODOT end --
 	  loopIndex++;
 #else
           yield();