libbb: introduce and use strcpy_and_process_escape_sequences

function                                             old     new   delta
strcpy_and_process_escape_sequences                    -      50     +50
bb_process_escape_sequence                           148     138     -10
printf_main                                          789     776     -13
getty_main                                          1897    1831     -66
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/3 up/down: 50/-89)            Total: -39 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/include/libbb.h b/include/libbb.h
index 409c434..c85dab2 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -324,6 +324,7 @@
 /* this helper yells "short read!" if param is not -1 */
 extern void complain_copyfd_and_die(off_t sz) NORETURN FAST_FUNC;
 extern char bb_process_escape_sequence(const char **ptr) FAST_FUNC;
+char* strcpy_and_process_escape_sequences(char *dst, const char *src) FAST_FUNC;
 /* xxxx_strip version can modify its parameter:
  * "/"        -> "/"
  * "abc"      -> "abc"