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/spawn_test.cpp b/tests/spawn_test.cpp
index dfce0dc..84df16d 100644
--- a/tests/spawn_test.cpp
+++ b/tests/spawn_test.cpp
@@ -96,6 +96,25 @@
   ASSERT_EQ(0, posix_spawnattr_destroy(&sa));
 }
 
+TEST(spawn, posix_spawnattr_setsigmask64_posix_spawnattr_getsigmask64) {
+  posix_spawnattr_t sa;
+  ASSERT_EQ(0, posix_spawnattr_init(&sa));
+
+  sigset64_t sigs;
+  ASSERT_EQ(0, posix_spawnattr_getsigmask64(&sa, &sigs));
+  ASSERT_FALSE(sigismember64(&sigs, SIGRTMIN));
+
+  sigset64_t just_SIGRTMIN;
+  sigemptyset64(&just_SIGRTMIN);
+  sigaddset64(&just_SIGRTMIN, SIGRTMIN);
+  ASSERT_EQ(0, posix_spawnattr_setsigmask64(&sa, &just_SIGRTMIN));
+
+  ASSERT_EQ(0, posix_spawnattr_getsigmask64(&sa, &sigs));
+  ASSERT_TRUE(sigismember64(&sigs, SIGRTMIN));
+
+  ASSERT_EQ(0, posix_spawnattr_destroy(&sa));
+}
+
 TEST(spawn, posix_spawnattr_setsigdefault_posix_spawnattr_getsigdefault) {
   posix_spawnattr_t sa;
   ASSERT_EQ(0, posix_spawnattr_init(&sa));
@@ -115,6 +134,25 @@
   ASSERT_EQ(0, posix_spawnattr_destroy(&sa));
 }
 
+TEST(spawn, posix_spawnattr_setsigdefault64_posix_spawnattr_getsigdefault64) {
+  posix_spawnattr_t sa;
+  ASSERT_EQ(0, posix_spawnattr_init(&sa));
+
+  sigset64_t sigs;
+  ASSERT_EQ(0, posix_spawnattr_getsigdefault64(&sa, &sigs));
+  ASSERT_FALSE(sigismember64(&sigs, SIGRTMIN));
+
+  sigset64_t just_SIGRTMIN;
+  sigemptyset64(&just_SIGRTMIN);
+  sigaddset64(&just_SIGRTMIN, SIGRTMIN);
+  ASSERT_EQ(0, posix_spawnattr_setsigdefault64(&sa, &just_SIGRTMIN));
+
+  ASSERT_EQ(0, posix_spawnattr_getsigdefault64(&sa, &sigs));
+  ASSERT_TRUE(sigismember64(&sigs, SIGRTMIN));
+
+  ASSERT_EQ(0, posix_spawnattr_destroy(&sa));
+}
+
 TEST(spawn, posix_spawnattr_setsschedparam_posix_spawnattr_getsschedparam) {
   posix_spawnattr_t sa;
   ASSERT_EQ(0, posix_spawnattr_init(&sa));