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;
 }