fix segfaults on OpenBSD: int cannot hold all the values a ptrdiff_t can take.

Change-Id: I90806e6f2e46a94f38aa0a8a7038aa6599b448b3
Reviewed-on: https://plan9port-review.googlesource.com/2660
Reviewed-by: Russ Cox <rsc@swtch.com>

src/libregexp/regcomp.c

diff --git a/src/libregexp/regcomp.c b/src/libregexp/regcomp.c
index 0967875..d9deb13 100644
--- a/src/libregexp/regcomp.c
+++ b/src/libregexp/regcomp.c
@@ -238,7 +238,7 @@
 	int size;
 	Reprog *npp;
 	Reclass *cl;
-	int diff;
+	ptrdiff_t diff;
 
 	/*
 	 *  get rid of NOOP chains