LibTest: Support death tests without child process cloning

A challenge for getting LibTest working on Windows has always
been CrashTest. It implements death tests similar to Google Test
where a child process is cloned to invoke the expression that
should abort/terminate the program. Then the exit code of the
child is used by the parent test process to verify if the
application correctly aborted/terminated due to invoking
the expression.

The problem was that finding an equivalent way to port Crash::run()
to Windows was not looking very likely as publicly exposed Win32/
Native APIs have no equivalent to fork(); however, Windows actually
does have native support for process cloning via undocumented NT
APIs that clever people reverse engineered and published, see
`NtCreateUserProcess()`.

All that being said, this `EXPECT_DEATH()` implementation avoids
needing to use a child process in general, allowing us to remove
CrashTest in favour of a single cross-platform solution for death
tests.

Tests/LibTest/TestNoCrash.cpp

@@ -8,7 +8,5 @@
 
 TEST_CASE(raise)
 {
-    EXPECT_NO_CRASH("This should never crash", [] {
-        return Test::Crash::Failure::DidNotCrash;
-    });
+    EXPECT_NO_DEATH("This should never crash", [] { }());
 }