ld: Add pdb support to aarch64-w64-mingw32

ld: Add pdb support to aarch64-w64-mingw32

This extends PDB support to the aarch64 PE targets.

The changes to the test files are just to make it so they can be assembled as
either x86, x86_64, or aarch64, mainly by changing the comment style.
The only actual code change here is in adding the architecture constants
to pdb.c.