Add missing dg-require-effective-target alloca.

Tested on nvptx.

2019-06-20  Tom de Vries  <tdevries@suse.de>

	* gcc.c-torture/compile/pr77754-1.c: Require alloca.
	* gcc.c-torture/compile/pr77754-2.c: Same.
	* gcc.c-torture/compile/pr77754-3.c: Same.
	* gcc.c-torture/compile/pr77754-4.c: Same.
	* gcc.c-torture/compile/pr77754-5.c: Same.
	* gcc.c-torture/compile/pr77754-6.c: Same.
	* gcc.c-torture/compile/pr87110.c: Same.
	* gcc.c-torture/execute/pr86528.c: Same.
	* gcc.dg/Walloca-larger-than-2.c: Same.
	* gcc.dg/Walloca-larger-than.c: Same.
	* gcc.dg/Warray-bounds-41.c: Same.
	* gcc.dg/Wrestrict-17.c: Same.
	* gcc.dg/Wstrict-overflow-27.c: Same.
	* gcc.dg/Wstringop-truncation-3.c: Same.
	* gcc.dg/pr78902.c: Same.
	* gcc.dg/pr87099.c: Same.
	* gcc.dg/pr87320.c: Same.
	* gcc.dg/pr89045.c: Same.
	* gcc.dg/strlenopt-62.c: Same.
	* gcc.dg/tree-ssa/alias-37.c: Same.

From-SVN: r272501