*: 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/selinux/chcon.c b/selinux/chcon.c
index 288e93a..505ae4f 100644
--- a/selinux/chcon.c
+++ b/selinux/chcon.c
@@ -28,7 +28,7 @@
 static char *range = NULL;
 static char *specified_context = NULL;
 
-static int change_filedir_context(
+static int FAST_FUNC change_filedir_context(
 		const char *fname,
 		struct stat *stbuf ATTRIBUTE_UNUSED,
 		void *userData ATTRIBUTE_UNUSED,