std: add fs::mkdir(), rng.gen_str(), tempfile::mkdtemp()

Signed-off-by: Elly Jones <elly@leptoquark.net>

src/lib/linux_os.rs

@@ -51,6 +51,7 @@ native mod libc {
     fn pipe(buf: *mutable fd_t) -> c_int;
     fn waitpid(pid: pid_t, &status: c_int, options: c_int) -> pid_t;
     fn readlink(path: str::sbuf, buf: str::sbuf, bufsize: size_t) -> ssize_t;
+    fn mkdir(path: str::sbuf, mode: int) -> int;
 }
 
 mod libc_constants {