[PATCH] Win64 SEH print register names

[Vadim Chugunov]

This patch doesn't work right.   I am seeing stuff like this in the emitted code: 
  	pushq	%rbp
  	.seh_pushreg %rdi
Which, I guess, makes sense, because MCAsmStreamer::EmitRegisterName performs DWARF->LLVM register index mapping before emitting the name.

If you are gonna try to fix this, please not that .seh_... directives seem to use "SEH" register numbers, which are probably different from normal LLVM register indices.

http://reviews.llvm.org/D3422