Some platforms use the same name for 32-bit and 64-bit registers (like

%r3 on PPC) in their ASM files. However, it's hard for humans to read
during debugging. Adding a new field to the register data that lets you
specify a different name to be printed than the one that goes into the
ASM file -- %x3 instead of %r3, for instance.

llvm-svn: 47534