Rollup merge of #135855 - cuviper:parser-size, r=wesleywiser

Only assert the `Parser` size on specific arches

The size of this struct depends on the alignment of `u128`, for example
powerpc64le and s390x have align-8 and end up with only 280 bytes. Our
64-bit tier-1 arches are the same though, so let's just assert on those.

r? nnethercote

Author: matthiaskrgr