[AIX] Support of Big archive (read)

[AIX] Support of Big archive (read)

Summary:

The patch is based on the EGuesnet's implement of the "Support of Big archive (read)
the first commit of the patch is come from https://reviews.llvm.org/D100651.

the rest of commits of the patch

1  Addressed the comments on the https://reviews.llvm.org/D100651
2  according to https://www.ibm.com/docs/en/aix/7.2?topic=formats-ar-file-format-big
using the "fl_fstmoff" for the first object file number, using "char ar_nxtmem[20]" to get next object file ,
using the "char fl_lstmoff[20]" for the last of the object file will fix the following problems:
   2.1 can not correct reading a archive files which has padding data between too object file
   2.2 can not correct reading a archive files from which some object file has be deleted

3 introduce a new derived class BigArchive for big ar file.

Reviewers: James Henderson
Differential Revision: https://reviews.llvm.org/D111889