No need to specialize DwarfInstructions::getCFA().  It is the same for all archs

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@207463 91177308-0d34-0410-b5e6-96231b3b80d8
Use return address register from CIE.  Move DwarfInstructions::lastRestoreReg() to Register::lastDwarfRegNum().

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@207467 91177308-0d34-0410-b5e6-96231b3b80d8
Fix cast warning

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@207469 91177308-0d34-0410-b5e6-96231b3b80d8