*: 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

libbb/ask_confirmation.c

@@ -13,7 +13,7 @@
 
 #include "libbb.h"
 
-int bb_ask_confirmation(void)
+int FAST_FUNC bb_ask_confirmation(void)
 {
 	int retval = 0;
 	int first = 1;