use strpbrk(3) to search for characters from a given set

We can check if certain characters are present in a string by calling
strchr(3) on each of them, or we can pass them all to a single
strpbrk(3) call.  The latter is shorter, less repetitive and slightly
more efficient, so let's do that instead.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/mingw.c

@@ -1232,7 +1232,7 @@ static char *path_lookup(const char *cmd, int exe_only)
 	int len = strlen(cmd);
 	int isexe = len >= 4 && !strcasecmp(cmd+len-4, ".exe");
 
-	if (strchr(cmd, '/') || strchr(cmd, '\\'))
+	if (strpbrk(cmd, "/\\"))
 		return xstrdup(cmd);
 
 	path = mingw_getenv("PATH");