[lld] [ELF] -r: Synthesize R_RISCV_ALIGN at input section start (PR #151639)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Renamed the `synthesizeAlign*` functions. They still feel clunky but are probably better than the initial version.

https://github.com/llvm/llvm-project/pull/151639