Rewrite system(3) to use posix_spawn(3).

We saw crashes from pthread_exit+debuggerd on LP32
(https://issuetracker.google.com/72291624), and it seems like the
equivalent problem should exist with system(3). I fixed posix_spawn(3)
as part of that bug, so the easiest fix is probably to reuse that.

Bug: http://b/72470344
Test: ran tests
Change-Id: I05f838706f2b4a14ac3ee21292833e6c8579b0d4
diff --git a/tests/SignalUtils.h b/tests/SignalUtils.h
new file mode 100644
index 0000000..ece28ba
--- /dev/null
+++ b/tests/SignalUtils.h
@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <signal.h>
+#include <string.h>
+
+#if defined(__GLIBC__)
+#define posix_spawnattr_getsigdefault64 posix_spawnattr_getsigdefault
+#define posix_spawnattr_getsigmask64 posix_spawnattr_getsigmask
+#define posix_spawnattr_setsigdefault64 posix_spawnattr_setsigdefault
+#define posix_spawnattr_setsigmask64 posix_spawnattr_setsigmask
+#define pthread_sigmask64 pthread_sigmask
+#define sigaction64 sigaction
+#define sigaddset64 sigaddset
+#define sigdelset64 sigdelset
+#define sigemptyset64 sigemptyset
+#define sigfillset64 sigfillset
+#define sigismember64 sigismember
+#define sigpending64 sigpending
+#define sigprocmask64 sigprocmask
+#define sigset64_t sigset_t
+#define sigsuspend64 sigsuspend
+#define sigtimedwait64 sigtimedwait
+#define sigwait64 sigwait
+#define sigwaitinfo64 sigwaitinfo
+#endif
+
+#include "private/ScopedSignalHandler.h"
+
+class SignalMaskRestorer {
+ public:
+  SignalMaskRestorer() {
+    sigprocmask64(SIG_SETMASK, nullptr, &old_mask_);
+  }
+
+  ~SignalMaskRestorer() {
+    sigprocmask64(SIG_SETMASK, &old_mask_, nullptr);
+  }
+
+ private:
+  sigset64_t old_mask_;
+};