This binds to the appropriate pthreads_* and Windows specific functions
and calls them from Rust. This allows for removal of the C++ support
code for threads.
Fixes#10162
This commit resumes management of the stack boundaries and limits when switching
between tasks. This additionally leverages the __morestack function to run code
on "stack overflow". The current behavior is to abort the process, but this is
probably not the best behavior in the long term (for deails, see the comment I
wrote up in the stack exhaustion routine).
