version: convert to parse-options

The "git version" command didn't traditionally accept any
options, and in fact ignores any you give it. When we added
simple option parsing for "--build-options" in 6b9c38e14, we
didn't improve this; we just loop over the arguments and
pick out the one we recognize.

Instead, let's move to a real parsing loop, complain about
nonsense options, and recognize conventions like "-h".

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

help.c

@@ -8,6 +8,7 @@
 #include "column.h"
 #include "version.h"
 #include "refs.h"
+#include "parse-options.h"
 
 void add_cmdname(struct cmdnames *cmds, const char *name, int len)
 {
@@ -424,16 +425,30 @@ const char *help_unknown_cmd(const char *cmd)
 
 int cmd_version(int argc, const char **argv, const char *prefix)
 {
+	int build_options = 0;
+	const char * const usage[] = {
+		N_("git version [<options>]"),
+		NULL
+	};
+	struct option options[] = {
+		OPT_BOOL(0, "build-options", &build_options,
+			 "also print build options"),
+		OPT_END()
+	};
+
+	argc = parse_options(argc, argv, prefix, options, usage, 0);
+
 	/*
 	 * The format of this string should be kept stable for compatibility
 	 * with external projects that rely on the output of "git version".
+	 *
+	 * Always show the version, even if other options are given.
 	 */
 	printf("git version %s\n", git_version_string);
-	while (*++argv) {
-		if (!strcmp(*argv, "--build-options")) {
-			printf("sizeof-long: %d\n", (int)sizeof(long));
-			/* NEEDSWORK: also save and output GIT-BUILD_OPTIONS? */
-		}
+
+	if (build_options) {
+		printf("sizeof-long: %d\n", (int)sizeof(long));
+		/* NEEDSWORK: also save and output GIT-BUILD_OPTIONS? */
 	}
 	return 0;
 }