Merge branch 'maint'

* maint:
  Unset NO_C99_FORMAT on Cygwin.
  Fix a "pointer type missmatch" warning.
  Fix some "comparison is always true/false" warnings.
  Fix an "implicit function definition" warning.
  Fix a "label defined but unreferenced" warning.
  Document the config variable format.suffix
  git-merge: fail correctly when we cannot fast forward.
  builtin-archive: use RUN_SETUP
  Fix git-gc usage note

builtin-archive.c

@@ -252,8 +252,6 @@ int cmd_archive(int argc, const char **argv, const char *prefix)
 
 	memset(&ar, 0, sizeof(ar));
 	tree_idx = parse_archive_args(argc, argv, &ar);
-	if (prefix == NULL)
-		prefix = setup_git_directory();
 
 	argv += tree_idx;
 	parse_treeish_arg(argv, &ar.args, prefix);