*: 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/libbb/run_shell.c b/libbb/run_shell.c
index 239887d..2ccb3a1 100644
--- a/libbb/run_shell.c
+++ b/libbb/run_shell.c
@@ -36,14 +36,12 @@
 #if ENABLE_SELINUX
 static security_context_t current_sid;
 
-void
-renew_current_security_context(void)
+void FAST_FUNC renew_current_security_context(void)
 {
 	freecon(current_sid);  /* Release old context  */
 	getcon(&current_sid);  /* update */
 }
-void
-set_current_security_context(security_context_t sid)
+void FAST_FUNC set_current_security_context(security_context_t sid)
 {
 	freecon(current_sid);  /* Release old context  */
 	current_sid = sid;
@@ -56,7 +54,7 @@
    If ADDITIONAL_ARGS is nonzero, pass it to the shell as more
    arguments.  */
 
-void run_shell(const char *shell, int loginshell, const char *command, const char **additional_args)
+void FAST_FUNC run_shell(const char *shell, int loginshell, const char *command, const char **additional_args)
 {
 	const char **args;
 	int argno = 1;