Add AutoUpgrade function to add new address space datalayout string to existing datalayouts.

Summary:
Add function to AutoUpgrade to change the datalayout of old X86 datalayout strings.
This adds "-p270:32:32-p271:32:32-p272:64:64" to X86 datalayouts that are otherwise valid
and don't already contain it.

This also removes the compatibility changes in https://reviews.llvm.org/D66843.
Datalayout change in https://reviews.llvm.org/D64931.

Reviewers: rnk, echristo

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67631

llvm-svn: 372267