*: introduce and use FAST_FUNC: regparm on i386, otherwise no-on

   text    data     bss     dec     hex filename
 808035     611    6868  815514   c719a busybox_old
 804472     611    6868  811951   c63af busybox_unstripped

diff --git a/archival/ar.c b/archival/ar.c
index 0a95e5c..ddc1209 100644
--- a/archival/ar.c
+++ b/archival/ar.c
@@ -16,7 +16,7 @@
 #include "libbb.h"
 #include "unarchive.h"
 
-static void header_verbose_list_ar(const file_header_t *file_header)
+static void FAST_FUNC header_verbose_list_ar(const file_header_t *file_header)
 {
 	const char *mode = bb_mode_string(file_header->mode);
 	char *mtime;