shells: do not frocibly enable test, echo and kill _applets_,

just build relevant source and use xxx_main functions.
build system: add a special case when we have exactly one applet enabled
(makes "true", "false", "basename" REALLY tiny).
getopt32: do not use stdio.

function                                             old     new   delta
getopt32                                            1385    1412     +27
make_device                                         1187    1200     +13
basename_main                                        120     127      +7
tcpudpsvd_main                                      1922    1926      +4
testcmd                                                5       -      -5
echocmd                                                5       -      -5
fuser_main                                          1243    1231     -12
------------------------------------------------------------------------------
(add/remove: 0/2 grow/shrink: 4/1 up/down: 51/-22)             Total: 29 bytes

1 files changed, 6 insertions, 5 deletions

diff --git a/coreutils/basename.c b/coreutils/basename.c
index d536a1bf3..ed2377948 100644
--- a/coreutils/basename.c
+++ b/coreutils/basename.c
@@ -37,15 +37,16 @@ int basename_main(int argc, char **argv)
 	/* It should strip slash: /abc/def/ -> def */
 	s = bb_get_last_path_component_strip(*++argv);
 
+	m = strlen(s);
 	if (*++argv) {
 		n = strlen(*argv);
-		m = strlen(s);
 		if ((m > n) && ((strcmp)(s+m-n, *argv) == 0)) {
-			s[m-n] = '\0';
+			m -= n;
+			s[m] = '\0';
 		}
 	}
 
-	puts(s);
-
-	return fflush(stdout);
+	/* puts(s) will do, but we can do without stdio this way: */
+	s[m++] = '\n';
+	return full_write(STDOUT_FILENO, s, m) == m;
 }