Add tracing to the tblgen register pressure table generator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187478 91177308-0d34-0410-b5e6-96231b3b80d8
Fix register pressure tables on ARM.

The heuristic that merges register pressure sets was bogus for ARM's S/D regs.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187479 91177308-0d34-0410-b5e6-96231b3b80d8