*: 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/util-linux/mdev.c b/util-linux/mdev.c
index e1edd20..bacccc0 100644
--- a/util-linux/mdev.c
+++ b/util-linux/mdev.c
@@ -299,7 +299,7 @@
 }
 
 /* File callback for /sys/ traversal */
-static int fileAction(const char *fileName,
+static int FAST_FUNC fileAction(const char *fileName,
 		struct stat *statbuf ATTRIBUTE_UNUSED,
 		void *userData,
 		int depth ATTRIBUTE_UNUSED)
@@ -319,7 +319,7 @@
 }
 
 /* Directory callback for /sys/ traversal */
-static int dirAction(const char *fileName ATTRIBUTE_UNUSED,
+static int FAST_FUNC dirAction(const char *fileName ATTRIBUTE_UNUSED,
 		struct stat *statbuf ATTRIBUTE_UNUSED,
 		void *userData ATTRIBUTE_UNUSED,
 		int depth)