Fixed Linux build with GL 3.1

src/renderer_gl.h

@@ -14,7 +14,9 @@
 #	if BGFX_CONFIG_RENDERER_OPENGL >= 31
 #		define GLCOREARB_PROTOTYPES
 #		include <gl/glcorearb.h>
-#		define GL_ARB_shader_objects // OSX collsion with GLhandleARB in gltypes.h
+#		if BX_PLATFORM_OSX
+#			define GL_ARB_shader_objects // OSX collsion with GLhandleARB in gltypes.h
+#		endif // BX_PLATFORM_OSX
 #	else
 #		if BX_PLATFORM_LINUX
 #			define GL_PROTOTYPES