[AIX][TLS] Account for local-exec accesses in XCOFFObjectWriter

This is a follow up to D149722 and aims to address https://github.com/llvm/llvm-project/issues/63885.
Local-exec accesses were not previously accounted for in XCOFFObjectWriter.
Specifically, the R_TLS_LE relocation was not previously handled, which lead to
the incorrect value being written for the relocation target.

Within this patch, the value being written is set to the symbol's virtual
address and extra relocation tests are added.

Differential Revision: https://reviews.llvm.org/D155415