Force redeclare of pthread_getstackaddr_np to avoid pointer truncation.
Clean up apple-specific SIGBUS checks.
Copy debugging symbols for i386 and x86_64.
Don't handle SIGSEGV on altstack on osx64 for now.
This fixes hard NRE handling.
Revert "removed signal exception handlers for amd64.  need to investigate why we did this, and if it can be restored to reduce upstream divergence."

This reverts commit 649a68ffc6568c27db188f6431e3507613f1eab9.
Merge branch 'mono-bisect' of github.com:Unity-Technologies/mono into mono-bisect