Needs ctype.h
Clang doesn't like when non-void functions use return; by itself.

Index: src/extspec.c
--- src/extspec.c.orig
+++ src/extspec.c
@@ -20,6 +20,7 @@
 
 /* TBD: Innlesing av identifikatorer mm m gjres mer robust. */
 
+#include <ctype.h>
 #include "const.h"
 #include "dekl.h"
 #include "filelist.h"
@@ -565,7 +566,7 @@ static void write_text_mif (FILE *f, unsigned char *s)
 /******************************************************************************
                                                               WRITE_DECL_MIF */
 
-static write_decl_mif (FILE *f, decl_t *rd, int level)
+static void write_decl_mif (FILE *f, decl_t *rd, int level)
 {
   if (rd->kind == KBLOKK || rd->kind == KPRBLK || rd->kind == KFOR || 
       rd->kind == KINSP) return;
