Fail to propagate magic1 field in signal frame (linux.sigcontext).

Looks to me like we're failing to propagate the magic1 field if the extended context is valid. The test for this is already been written (linux.sigcontext), but the AVX part is not enabled by default. When tweaking the test, it looks like we're good propagating the state, but we're not setting the magic1 field, which the test already checks. The same might apply to magic2, I'm not sure if that gets copied already or needs to be written separately.

To be clear, the issue is only exposed when editing the test and make sure it's compiled with and include AVX state.