*.c static functions: add missing __attribute__((format))

Add missing __attribute__((format)) function attributes to various
"static" functions that take printf arguments.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

worktree.c

@@ -265,6 +265,7 @@ const char *worktree_prune_reason(struct worktree *wt, timestamp_t expire)
 }
 
 /* convenient wrapper to deal with NULL strbuf */
+__attribute__((format (printf, 2, 3)))
 static void strbuf_addf_gently(struct strbuf *buf, const char *fmt, ...)
 {
 	va_list params;