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.

archival/libunarchive/decompress_unzip.c

@@ -64,6 +64,7 @@ static char *license_msg[] = {
 #include <sys/wait.h>
 #include <signal.h>
 #include <stdlib.h>
+#include <string.h>
 #include "libbb.h"
 
 FILE *in_file, *out_file;