Compile and warning cleanup

src/backend/regex/regerror.c

@@ -47,6 +47,7 @@ static char sccsid[] = "@(#)regerror.c	8.4 (Berkeley) 3/20/94";
 #include <ctype.h>
 #include <limits.h>
 #include <stdlib.h>
+#include <assert.h>
 
 #include <regex/regex.h>
 #include <regex/utils.h>