MFC r322368, r322371:

MFC r322368, r322371:
fnmatch(3): improve POSIX conformance.

In a recent interpretation[1], "\\" shall return a non-zero value
(indicating either no match or an error).

The fix involves a change over r254091 and now the behavior matches the
Sun/IBM/HP closed source implementations and also likely musl libc.

Submitted by:	Joerg Schilling <joerg at schily.net>

[1] http://austingroupbugs.net/view.php?id=806

git-svn-id: svn://svn.freebsd.org/base/stable/10@324505 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f