[Sanitizer] Fix getpwnam test on ppc64le Fedora 21.

Summary:
On ppc64le Fedora 21, getpwnam_r("no-such-user", ...) returns ENOENT
instead of 0. Tolerate this in the test case.

Reviewers: eugenis

Reviewed By: eugenis

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9233

llvm-svn: 235654