Fix error in_death_test_child_process: undeclared identifier

[sergio-nsk]

The error occurs if !GTEST_HAS_DEATH_TEST on Windows.

I could not make the change better. If I make

bool in_death_test_child_process = false;
#if GTEST_HAS_DEATH_TEST
  in_death_test_child_process =
      GTEST_FLAG_GET(internal_run_death_test).length() > 0;

then the error about an assigned but unused variable occurs on Linux.

[horenmar]

I think the fix in #4165 (implemented for microsoft/vcpkg#29772) is better.

[sergio-nsk]

@horenmar The fix with #if GTEST_OS_WINDOWS && GTEST_HAS_DEATH_TEST completely excludes the code block that tunes output to stderr not only for death tests. IMHO it's not correct.