Fixed #1831.

src/renderer_gl.h

@@ -949,6 +949,10 @@ typedef uint64_t GLuint64;
 #	define GL_BUFFER 0x82E0
 #endif // GL_BUFFER
 
+#ifndef GL_COMMAND_BARRIER_BIT
+#	define GL_COMMAND_BARRIER_BIT 0x00000040
+#endif // GL_COMMAND_BARRIER_BIT
+
 // _KHR or _ARB...
 #define GL_DEBUG_OUTPUT_SYNCHRONOUS         0x8242
 #define GL_DEBUG_NEXT_LOGGED_MESSAGE_LENGTH 0x8243