Fix Platform Thread Override

core/os/thread.cpp

@@ -28,9 +28,7 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
 /*************************************************************************/
 
-// Define PLATFORM_CUSTOM_THREAD_H in platform_config.h
-// Overriding the platform implementation is required in some proprietary platforms
-#ifndef PLATFORM_CUSTOM_THREAD_H
+#ifndef PLATFORM_THREAD_OVERRIDE // See details in thread.h
 
 #include "thread.h"
 
@@ -130,4 +128,4 @@ Thread::~Thread() {
 }
 
 #endif
-#endif // PLATFORM_CUSTOM_THREAD_H
+#endif // PLATFORM_THREAD_OVERRIDE