Add dump of Win64 EH unwind data.

The new command line option -unwind-info dumps the Win64 EH unwind
data to the console. This is a nice feature if you need to debug
generated EH data (e.g. from LLVM). Includes a test case.

Initial patch by João Matos, extensions and rework by Kai Nacke.

llvm-svn: 169415