Add a relocation to ObjectFileELF::ApplyRelocations and a test

Summary:
pcm files can end up being processed by lldb with relocations to be
made for the .debug_info section. When a R_AARCH64_ABS64 relocation
was required lldb would hit an `assert(false)` and die.

Add R_AARCH64_ABS64 relocations to the S+A 64 bit width code path. Add
a test for R_AARCH64_ABS64 and R_AARCH64_ABS32 .rela.debug_info
relocations in a pcm file.

Reviewers: sas, xiaobai, davide, javed.absar, espindola

Reviewed By: davide

Subscribers: labath, zturner, emaste, mgorny, arichardson, kristof.beyls

Differential Revision: https://reviews.llvm.org/D51566

llvm-svn: 346171