pair instead of from a virtual method on TargetMachine. This cuts the final
ties of TargetAsmInfo to TargetMachine, meaning that MC can now use
TargetAsmInfo.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78802 91177308-0d34-0410-b5e6-96231b3b80d8