According to POSIX \ in the fnmatch(3) pattern should escape

any character including '\0', but our version replace escaped '\0'
with '\\'.
I.e. fnmatch("\\", "\\", 0) should not match while fnmatch("\\", "", 0)
should (Linux and NetBSD does the same). Was vice versa.

PR:     181129
MFC after:      1 week

lib/libc/gen/fnmatch.c

@@ -194,8 +194,6 @@ fnmatch1(pattern, string, stringstart, flags, patmbs, strmbs)
 				    &patmbs);
 				if (pclen == (size_t)-1 || pclen == (size_t)-2)
 					return (FNM_NOMATCH);
-				if (pclen == 0)
-					pc = '\\';
 				pattern += pclen;
 			}
 			/* FALLTHROUGH */