[test] [filesystems] Extend FreeBSD tv_sec==-1 workaround to NetBSD

NetBSD also uses tv_sec==-1 as error status indicator, and does not
support setting such a value.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@348967 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed