Since we have moved unified assembly, switch to ADR instruction instead of a...

Since we have moved unified assembly, switch to ADR instruction instead of a the difficult-to-read .set + add syntax to materialize pc-relative address.

Turns out this also fixed a poor code selection on Thumb1. I have no idea why we were using a mov + add to do the same thing as ADR before.

llvm-svn: 76889