[AsyncToLLVM] Align frames to 64 bytes

Coroutine lowering always takes the natural alignment when spilling to
the frame (issue #53148) so using AVX2 or AVX512 in a coroutine doesn't
work. Always overalign to 64 bytes to avoid this issue until we have a
better solution.

Differential Revision: https://reviews.llvm.org/D117501