[AArch64] Support COFF linker directives

This is similar to what was done for ARM in SVN r269574; the code
and the test are straight copypaste to the corresponding AArch64
code and test directory.

Differential revision: https://reviews.llvm.org/D37204

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@312223 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed