*: 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/remove_file.c

@@ -11,7 +11,7 @@
 
 /* Used from NOFORK applets. Must not allocate anything */
 
-int remove_file(const char *path, int flags)
+int FAST_FUNC remove_file(const char *path, int flags)
 {
 	struct stat path_stat;