[PowerPC][AIX] Adds support for writing the data section in object files
Adds support for generating the XCOFF data section in object files for global variables with initialization.
Merged aix-xcoff-common.ll into aix-xcoff-data.ll.
Changed variable name charr to chrarray in the test case to test if readobj works with 8-character names.
Authored by: xingxue
Reviewers: hubert.reinterptrtcast, sfertile, jasonliu, daltenty, Xiangling_L.
Reviewed by: hubert.reinterpretcast, sfertile, daltenty.
Subscribers: DiggerLin, Wuzish, nemanjai, hiraditya, MaskRay, jsji, shchenz, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D67125