libobs-opengl: Rename gl-x11.c to gl-x11-glx.c

This is in preparation for the future abstraction layer (gl-x11-*)
and also to match the actual name of the windowing system. When
running under X11, we can glue OpenGL through GLX or EGL, so the
new file name matches that now.

libobs-opengl/CMakeLists.txt

@@ -45,7 +45,7 @@ else() #This needs to change to be more specific to get ready for Wayland
 		${X11_XCB_LIBRARIES})
 
 	set(libobs-opengl_PLATFORM_SOURCES
-		gl-x11.c)
+		gl-x11-glx.c)
 endif()
 
 set(libobs-opengl_SOURCES