correctly: skipping instructions by incorrectly incrementing the pointer.
Also adds support for building a reg-to-regclass map, and splits the function
for saving register to stack into two, one suitable for virtual registers
(which also assigns it a physical register) and one for simply storing back
physical registers.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@4898 91177308-0d34-0410-b5e6-96231b3b80d8
