Add some missing includes to kill warnings when building with the default

Config.h and using gcc's -fno-builtin.  There are probably other files
with the similar problems.
Also, if building against uClibc, don't include asm/unistd.h in syscalls.c
and module_syscalls.c.

coreutils/rm.c

@@ -29,6 +29,7 @@
 #include <errno.h>
 #include <unistd.h>
 #include <stdlib.h>
+#include <string.h>
 #include <getopt.h>
 #include "busybox.h"