[X86] Use llvm::Align for passing the alignment

This should be a typo in `emitConstantSizeRepmov`. Both its caller and
callee store the alignment in a 64-bit variables, no reason to truncate
it to 32-bit. It results in alignment turns into 0 when larger than
0x100000000.

Fixes #61348

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D145863