Adjust type of mono_win_vectored_exception_handle to match its use.

This commit licensed as MIT/X11.
Mark some functions as static.

This commit licensed as MIT/X11.
Move a variable declaration to the start of a block.

This commit licensed as MIT/X11.
Fix MonoW32ExceptionHandler type on win64.

This commit licensed as MIT/X11.
Merge pull request #831 from madewokherd/win64-warnings

fix various warnings in win64 exception code