Add more missing config.h includes

config.h includes were missing in a few files, including input.c, the
lack of which caused the X11 backend to segfault instantly due to not
having an xkbcommon context.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>
diff --git a/src/launcher-util.h b/src/launcher-util.h
index da11028..c79b47c 100644
--- a/src/launcher-util.h
+++ b/src/launcher-util.h
@@ -23,6 +23,8 @@
 #ifndef _WESTON_LAUNCHER_UTIL_H_
 #define _WESTON_LAUNCHER_UTIL_H_
 
+#include "config.h"
+
 #include "compositor.h"
 
 int