Fix alignment of thunks for ARM/ARM64

The alignment of ARM64 range extension thunks was fixed in
7c816492, but ARM range extension thunks, and import
and delay import thunks also need aligning (like all code on ARM
platforms).

I'm adding a test for alignment of ARM64 import thunks - not
specifically adding tests for misalignment of all of them though.

Differential Revision: https://reviews.llvm.org/D77796

(cherry picked from commit 12c9e2f1)