*: 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/info_msg.c b/libbb/info_msg.c
index 3231bc8..ffef05e 100644
--- a/libbb/info_msg.c
+++ b/libbb/info_msg.c
@@ -10,7 +10,7 @@
 #include "libbb.h"
 #include <syslog.h>
 
-void bb_info_msg(const char *s, ...)
+void FAST_FUNC bb_info_msg(const char *s, ...)
 {
 	va_list p;
 	/* va_copy is used because it is not portable