portability: allow building in systems without d_type

Since 09fb155 (diff --no-index: support limiting by pathspec,
2025-05-21) git fails to build on platforms that don't have a
d_type member on their struct dirent (ex: AIX, NonStop).

Use the DTYPE() macro instead of a direct reference to d_type.

Signed-off-by: Carlo Marcelo Arenas Belón <[email protected]>
Reviewed-by: Collin Funk <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: carenas

diff-no-index.c

@@ -46,7 +46,7 @@ static int read_directory_contents(const char *path, struct string_list *list,
 
 			if (!match_leading_pathspec(NULL, pathspec,
 						    match.buf, match.len,
-						    0, NULL, e->d_type == DT_DIR ? 1 : 0))
+						    0, NULL, DTYPE(e) == DT_DIR ? 1 : 0))
 				continue;
 		}