Remove WLR_HAS_XCB_ERRORS

wlroots' dependency on this library doesn't change the features
exposed to compositors. It's purely a wlroots implementation detail.
Thus downstream compositors shouldn't really care about it.

Introduce an "internal_features" dictionary to store the status of
such internal dependencies.

include/backend/x11.h

@@ -9,7 +9,7 @@
 #include <xcb/xcb.h>
 #include <xcb/present.h>
 
-#if WLR_HAS_XCB_ERRORS
+#if HAS_XCB_ERRORS
 #include <xcb/xcb_errors.h>
 #endif
 
@@ -103,7 +103,7 @@ struct wlr_x11_backend {
 	// The time we last received an event
 	xcb_timestamp_t time;
 
-#if WLR_HAS_XCB_ERRORS
+#if HAS_XCB_ERRORS
 	xcb_errors_context_t *errors_context;
 #endif
 

include/wlr/config.h.in

@@ -10,8 +10,6 @@
 
 #mesondefine WLR_HAS_XWAYLAND
 
-#mesondefine WLR_HAS_XCB_ERRORS
-
 #mesondefine WLR_HAS_XDG_FOREIGN
 
 #endif

include/xwayland/xwm.h

@@ -5,7 +5,7 @@
 #include <wlr/config.h>
 #include <wlr/xwayland.h>
 #include <xcb/render.h>
-#if WLR_HAS_XCB_ERRORS
+#if HAS_XCB_ERRORS
 #include <xcb/xcb_errors.h>
 #endif
 #include "xwayland/selection.h"
@@ -113,7 +113,7 @@ struct wlr_xwm {
 	struct wlr_xwayland_surface *drag_focus;
 
 	const xcb_query_extension_reply_t *xfixes;
-#if WLR_HAS_XCB_ERRORS
+#if HAS_XCB_ERRORS
 	xcb_errors_context_t *errors_context;
 #endif
 	unsigned int last_focus_seq;