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

[Fangrui Song via llvm-commits]

MaskRay wrote:

I have a more detailed write-up here :) 
https://maskray.me/blog/2021-03-14-the-dark-side-of-riscv-linker-relaxation#:~:text=relocatable

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