[AIX][XCOFF] parsing xcoff object file auxiliary header

Summary:

The patch supports parsing the xcoff object file auxiliary header with llvm-readobj with option "auxiliary-headers"

the format of auxiliary header as
https://www.ibm.com/support/knowledgecenter/en/ssw_aix_72/filesreference/XCOFF.html#XCOFF__fyovh386shar

Reviewers: James Henderson, Jason Liu, Hubert Tong, Esme yi, Sean Fertile.

Differential Revision: https://reviews.llvm.org/D82549