Emit the LLVM<->DWARF register mapping as a sorted table and use binary search to do the lookup.

This also avoids emitting the information twice, which led to code bloat. On i386-linux-Release+Asserts
with all targets built this change shaves a whopping 1.3 MB off clang. The number is probably exaggerated
by recent inliner changes but the methods were already enormous with the old inline cost computation.

The DWARF reg -> LLVM reg mapping doesn't seem to have holes in it, so it could be a simple lookup table.
I didn't implement that optimization yet to avoid potentially changing functionality.

There is still some duplication both in tablegen and the generated code that should be cleaned up eventually.

llvm-svn: 153837