[libc] Use ASSERT_DEATH for EXPECT_DEATH under Fuchsia zxtest

[mcgrathr]

Summary

The Fuchsia zxtest library has ASSERT_DEATH but not EXPECT_DEATH.
The latter may be added in the future, but for now just use the
former as substitute.

[abrachet]

I'm guessing because you called it FUNC that llvm-libc's unittest framework takes a callable object and not an expression like gtest.

Should we also wrap this like [&]{ ASSERT_DEATH(FUNC, SIG); }() so EXPECT_DEATH can be used in function with returns non void?

[mcgrathr]

In D156940#4555479, @abrachet wrote:

I'm guessing because you called it FUNC that llvm-libc's unittest framework takes a callable object and not an expression like gtest.

Correct.

Should we also wrap this like [&]{ ASSERT_DEATH(FUNC, SIG); }() so EXPECT_DEATH can be used in function with returns non void?

Good idea.

[mcgrathr]

Wrap in a lambda to swallow early returns.

libc/test/UnitTest/FuchsiaTest.h

 //===-- Header for setting up the Fuchsia tests -----------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIBC_UTILS_UNITTEST_FUCHSIATEST_H
 #define LLVM_LIBC_UTILS_UNITTEST_FUCHSIATEST_H
 
 #include <zxtest/zxtest.h>
 
 #define WITH_SIGNAL(X) #X
 
+#ifndef EXPECT_DEATH
+// Since zxtest has ASSERT_DEATH but not EXPECT_DEATH, wrap calling it
+// in a lambda returning void to swallow any early returns so that this
+// can be used in a function that itself returns non-void.
+#define EXPECT_DEATH(FUNC, SIG) ([&] { ASSERT_DEATH(FUNC, SIG); }())
+#endif
+
 namespace __llvm_libc::testing {
 using Test = ::zxtest::Test;
 }
 
 #endif // LLVM_LIBC_UTILS_UNITTEST_FUCHSIATEST_H