[MS ABI] Hook clang up to the new EH instructions

The new EH instructions make it possible for LLVM to generate .xdata
tables that the MSVC personality routines will be happy about.  Because
this is experimental, hide it behind a -cc1 flag (-fnew-ms-eh).

Differential Revision: http://reviews.llvm.org/D11405

llvm-svn: 243767