[LLDB] Fix FreeBSD build.
To align with the LaunchThread change.
Reviewers: MaskRay, mgorny
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D64398
@devnexen this appears to cause https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=241137, where simply launching a process in lldb triggers a failure:
Expected<T> must be checked before access or destruction. Expected<T> value was in success state. (Note: Expected<T> values in success mode must still be checked prior to being destroyed).
This is occurring when calling operator-> in this part:
792 if (m_operation_thread->IsJoinable()) 793 return;
Btw, note that this only happens when LLVM_ENABLE_ABI_BREAKING_CHECKS is on, but it is not entirely clear to me where that gets toggled. We have it in our pre-generated headers though, so it must come originally from some CMake logic...