Fork as early as possible

If fork is requested, we fork as early as possible, way before anything
is initialized. This way, we don't need to do the gymnastics to make
OpenGL work properly across fork.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/config.h

@@ -96,8 +96,6 @@ typedef struct options_t {
 	bool glx_use_gpushader4;
 	/// Custom fragment shader for painting windows, as a string.
 	char *glx_fshader_win_str;
-	/// Whether to fork to background.
-	bool fork_after_register;
 	/// Whether to detect rounded corners.
 	bool detect_rounded_corners;
 	/// Force painting of window content with blending.