*: 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/bb_askpass.c b/libbb/bb_askpass.c
index 3ad0e97..ca18ade 100644
--- a/libbb/bb_askpass.c
+++ b/libbb/bb_askpass.c
@@ -17,7 +17,7 @@
 {
 }
 
-char *bb_askpass(int timeout, const char *prompt)
+char* FAST_FUNC bb_askpass(int timeout, const char *prompt)
 {
 	/* Was static char[BIGNUM] */
 	enum { sizeof_passwd = 128 };