*: 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/findutils/grep.c b/findutils/grep.c
index 9792ce4..8d18f43 100644
--- a/findutils/grep.c
+++ b/findutils/grep.c
@@ -370,7 +370,7 @@
 	}
 }
 
-static int file_action_grep(const char *filename,
+static int FAST_FUNC file_action_grep(const char *filename,
 			struct stat *statbuf ATTRIBUTE_UNUSED,
 			void* matched,
 			int depth ATTRIBUTE_UNUSED)