Rollup merge of #144578 - FractalFir:m68k_fix, r=compiler-errors

Ensure correct aligement of rustc_hir::Lifetime on platforms with lower default alignments.

The compiler relies on `hir::Lifetime` being aligned to at least 4 bytes(for the purposes of pointer tagging).

However, on some systems(like m68k) with lower alignment requirements(eg. usize / u32 aligned to 2 bytes),`hir::Lifetime` will be aligned to only 2 bytes.

This causes the compilation to fail on those systems - a const assert in the compiler fails.

This PR makes the aligement requriement of hir::Lifetime explict. This has no effect on platforms where that already is the case(repr align can only raise alignment), but ensures the alignment will stay correct no matter what.

Author: Zalathar