[testsuite] Add missing function decl to regs-arg-size.c

2018-02-26  Tom de Vries  <tom@codesourcery.com>

	* gcc.c-torture/compile/regs-arg-size.c (swprintf): Declare.

From-SVN: r257994

gcc/testsuite/ChangeLog

+2018-02-26  Tom de Vries  <tom@codesourcery.com>
+
+	* gcc.c-torture/compile/regs-arg-size.c (swprintf): Declare.
+
 2018-02-26  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR target/84530

gcc/testsuite/gcc.c-torture/compile/regs-arg-size.c

 int foo;
 typedef long unsigned int size_t;
 typedef short unsigned int wchar_t;
+extern int swprintf (wchar_t *wcs, size_t maxlen, const wchar_t *format, ...);
 struct tm
 {
   int tm_mday;