configfile.c: don't include system headers directly

git-compat-util.h may define various values that affect the
interpretation of system headers.  In most places we include cgit.h
first, which pulls in git-compat-util.h, but this file does not depend
on anything else in CGit, so use git-compat-util.h directly.

Signed-off-by: John Keeping <john@keeping.me.uk>

configfile.c

@@ -6,8 +6,7 @@
  *   (see COPYING for full license text)
  */
 
-#include <ctype.h>
+#include <git-compat-util.h>
-#include <stdio.h>
 #include "configfile.h"
 
 static int next_char(FILE *f)