configure: fix escaping in xcb cflags / libs

Fixes build with open64
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -5040,8 +5040,8 @@ if enabled libxcb; then
             enabled libxcb_xfixes && die "ERROR: libxcb_xfixes not found";
         } && enable libxcb_xfixes; }
 
-    add_cflags "$xcb_event_cflags $xcb_shm_cflags $xcb_xfixes_cflags"
-    add_extralibs "$xcb_event_libs $xcb_shm_libs $xcb_xfixes_libs"
+    add_cflags $xcb_event_cflags $xcb_shm_cflags $xcb_xfixes_cflags
+    add_extralibs $xcb_event_libs $xcb_shm_libs $xcb_xfixes_libs
 fi
 fi