BUG_exit_code: fix sparse "symbol not declared" warning

Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-compat-util.h

@@ -1111,6 +1111,9 @@ static inline int regexec_buf(const regex_t *preg, const char *buf, size_t size,
 #define HAVE_VARIADIC_MACROS 1
 #endif
 
+/* usage.c: only to be used for testing BUG() implementation (see test-tool) */
+extern int BUG_exit_code;
+
 #ifdef HAVE_VARIADIC_MACROS
 __attribute__((format (printf, 3, 4))) NORETURN
 void BUG_fl(const char *file, int line, const char *fmt, ...);

t/helper/test-tool.c

@@ -47,7 +47,6 @@ static struct test_cmd cmds[] = {
 int cmd_main(int argc, const char **argv)
 {
 	int i;
-	extern int BUG_exit_code;
 
 	BUG_exit_code = 99;
 	if (argc < 2)