Backport r265322 from llvm upstream

Since x86 psABIs require the function incoming stack must align at 16
bytes, child process stack passed to clone should be aligned at 16
bytes.

	PR testsuite/70520
	* c-c++-common/asan/clone-test-1.c (main): Align child process
	stack to 16 bytes.

From-SVN: r235790