syscall: ensure openat uses variadic libc wrapper

On powerpc64le, this caused a failure in TestUnshareUidGidMapping
due to stack corruption which resulted in a bogus execve syscall.

Use the existing c wrapper to ensure we respect the ppc abi for
variadic functions.

Fixes https://gcc.gnu.org/PR98610

Change-Id: I29a7c8d8776bb50a9973b3e2794e5fafaf138caa
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/282717
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Cherry Zhang <cherryyz@google.com>
1 file changed