*: 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/trim.c

@@ -10,7 +10,7 @@
 
 #include "libbb.h"
 
-void trim(char *s)
+void FAST_FUNC trim(char *s)
 {
 	size_t len = strlen(s);
 	size_t lws;