[PATCH - 5.8.9] Fix build warning from Change 34974

Change 34974 to scope.c produces the following build warning:

scope.c: In function `Perl_leave_scope':
scope.c:623: warning: ISO C90 forbids mixed declarations and code

The attached patch fixes this.

• [PATCH - 5.8.9] Fix build warning from Change 34974 by Jerry D. Hedden
• Re: [PATCH - 5.8.9] Fix build warning from Change 34974 by Nicholas Clark