build: fix build error with __ANDROID_API__ < 21

Fix the following undefined symbols error with __ANDROID_API__ < 21:
- epoll_create1
- epoll_pwait
- futimens

src/unix/fs.c

@@ -216,7 +216,11 @@ static ssize_t uv__fs_futime(uv_fs_t* req) {
   ts[0].tv_nsec = (uint64_t)(req->atime * 1000000) % 1000000 * 1000;
   ts[1].tv_sec  = req->mtime;
   ts[1].tv_nsec = (uint64_t)(req->mtime * 1000000) % 1000000 * 1000;
+#if defined(__ANDROID_API__) && __ANDROID_API__ < 21
+  return utimensat(req->file, NULL, ts, 0);
+#else
   return futimens(req->file, ts);
+#endif
 #elif defined(__APPLE__)                                                      \
     || defined(__DragonFly__)                                                 \
     || defined(__FreeBSD__)                                                   \

src/unix/linux-core.c

@@ -90,7 +90,12 @@ int uv__platform_loop_init(uv_loop_t* loop) {
    * a.k.a. Lollipop. Since EPOLL_CLOEXEC is an alias for O_CLOEXEC on all
    * architectures, we just use that instead.
    */
+#if defined(__ANDROID_API__) && __ANDROID_API__ < 21
+  fd = -1;
+  errno = ENOSYS;
+#else
   fd = epoll_create1(O_CLOEXEC);
+#endif
 
   /* epoll_create1() can fail either because it's not implemented (old kernel)
    * or because it doesn't understand the O_CLOEXEC flag.
@@ -288,11 +293,16 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
         abort();
 
     if (no_epoll_wait != 0 || (sigmask != 0 && no_epoll_pwait == 0)) {
+#if defined(__ANDROID_API__) && __ANDROID_API__ < 21
+      nfds = -1;
+      errno = ENOSYS;
+#else
       nfds = epoll_pwait(loop->backend_fd,
                          events,
                          ARRAY_SIZE(events),
                          timeout,
                          &sigset);
+#endif
       if (nfds == -1 && errno == ENOSYS)
         no_epoll_pwait = 1;
     } else {