Add `sigset64_t` and accompanying functions.

This doesn't address `struct sigaction` and `sigaction`. That will
come later.

Bug: http://b/72493232
Test: ran tests
Change-Id: I4134346757ce3a4dac6feae413361cec16223386
diff --git a/tests/sys_signalfd_test.cpp b/tests/sys_signalfd_test.cpp
new file mode 100644
index 0000000..67a72e0
--- /dev/null
+++ b/tests/sys_signalfd_test.cpp
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <gtest/gtest.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <sys/signalfd.h>
+#include <unistd.h>
+
+#include <thread>
+
+#include "ScopedSignalHandler.h"
+
+static void TestSignalFd(int fd, int signal) {
+  ASSERT_NE(-1, fd) << strerror(errno);
+
+  ASSERT_EQ(0, raise(signal));
+
+  signalfd_siginfo sfd_si;
+  ASSERT_EQ(static_cast<ssize_t>(sizeof(sfd_si)), read(fd, &sfd_si, sizeof(sfd_si)));
+
+  ASSERT_EQ(signal, static_cast<int>(sfd_si.ssi_signo));
+
+  close(fd);
+}
+
+TEST(sys_signalfd, signalfd) {
+  SignalMaskRestorer smr;
+
+  sigset_t mask = {};
+  sigaddset(&mask, SIGALRM);
+  ASSERT_EQ(0, sigprocmask(SIG_SETMASK, &mask, nullptr));
+
+  TestSignalFd(signalfd(-1, &mask, SFD_CLOEXEC), SIGALRM);
+}
+
+TEST(sys_signalfd, signalfd64) {
+#if defined(__BIONIC__)
+  SignalMaskRestorer smr;
+
+  sigset64_t mask = {};
+  sigaddset64(&mask, SIGRTMIN);
+  ASSERT_EQ(0, sigprocmask64(SIG_SETMASK, &mask, nullptr));
+
+  TestSignalFd(signalfd64(-1, &mask, SFD_CLOEXEC), SIGRTMIN);
+#endif
+}