test: fix spawn_stdout_and_stderr_to_file test

S_IREAD and S_IWRITE are obsolete in GNU libs and
not included in the Android NDK's libc. See
http://www.gnu.org/savannah-checkouts/gnu/libc
/manual/html_node/Permission-Bits.html

test/test-spawn.c

@@ -290,7 +290,7 @@ TEST_IMPL(spawn_stdout_and_stderr_to_file) {
   init_process_options("spawn_helper6", exit_cb);
 
   r = uv_fs_open(uv_default_loop(), &fs_req, "stdout_file", O_CREAT | O_RDWR,
-      S_IREAD | S_IWRITE, NULL);
+      S_IRUSR | S_IWUSR, NULL);
   ASSERT(r != -1);
   uv_fs_req_cleanup(&fs_req);