pathspec: use BUG(...) not die("BUG:%s:%d....", <file>, <line>)

Change code that was added in 8f4f8f4579f (guard against new pathspec
magic in pathspec matching code, 2013-07-14) to use the BUG() macro
instead of emitting a "fatal" message with the "__FILE__"-name and
"__LINE__"-numbers.

The original code predated the existence of the BUG() function, which
was added in d8193743e08 (usage.c: add BUG() function, 2017-05-12).

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/tree-diff.c b/tree-diff.c
index 437c98a..69031d7 100644
--- a/tree-diff.c
+++ b/tree-diff.c
@@ -603,8 +603,7 @@ static void try_to_follow_renames(const struct object_id *old_oid,
 	 * about dry-run mode and returns wildcard info.
 	 */
 	if (opt->pathspec.has_wildcard)
-		die("BUG:%s:%d: wildcards are not supported",
-		    __FILE__, __LINE__);
+		BUG("wildcards are not supported");
 #endif
 
 	/* Remove the file creation entry from the diff queue, and remember it */