[VE] Correct stack alignment

Summary:
Change stack alignment from 64 bits to 128 bits to follow ABI correctly.
And add a regression test for datalayout.

Reviewers: simoll, k-ishizaka

Reviewed By: simoll

Subscribers: hiraditya, cfe-commits, llvm-commits

Tags: #llvm, #ve, #clang

Differential Revision: https://reviews.llvm.org/D83173