bbconfig: make it independent from printf functions

function                                             old     new   delta
full_write2_str                                        -      25     +25
full_write1_str                                        -      25     +25
clear_main                                            21      20      -1
telnet_main                                         1488    1477     -11
getty_main                                          1932    1918     -14
full_write22_str                                      25       -     -25
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 0/3 up/down: 50/-51)             Total: -1 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/include/libbb.h b/include/libbb.h
index 3fffa83..22c72d9 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -674,6 +674,8 @@
 extern ssize_t full_write(int fd, const void *buf, size_t count) FAST_FUNC;
 extern void xwrite(int fd, const void *buf, size_t count) FAST_FUNC;
 extern void xwrite_str(int fd, const char *str) FAST_FUNC;
+extern ssize_t full_write1_str(const char *str) FAST_FUNC;
+extern ssize_t full_write2_str(const char *str) FAST_FUNC;
 extern void xopen_xwrite_close(const char* file, const char *str) FAST_FUNC;
 
 /* Close fd, but check for failures (some types of write errors) */