Add nullability annotations to FTS::fts_compare.

clang gets annoyed if you don't annotate _every_ pointer in a file; make the struct field match the function pointer type fts_open() accepts.

Bug: http://b/396699443
Change-Id: I612129162fbe19dded618a36c1e44d7ff9b9b4dc
diff --git a/libc/include/fts.h b/libc/include/fts.h
index ac3ecc8..69e17df 100644
--- a/libc/include/fts.h
+++ b/libc/include/fts.h
@@ -98,7 +98,7 @@
 	int fts_rfd;			/* fd for root */
 	size_t fts_pathlen;		/* sizeof(path) */
 	int fts_nitems;			/* elements in the sort array */
-	int (* _Nullable fts_compar)(const FTSENT **, const FTSENT **);		/* compare function */
+	int (* _Nullable fts_compar)(const FTSENT* _Nonnull * _Nonnull, const FTSENT* _Nonnull * _Nonnull);		/* compare function */
 
 #define	FTS_COMFOLLOW	0x0001		/* follow command line symlinks */
 #define	FTS_LOGICAL	0x0002		/* logical walk */