[lld] [lld][COFF] Add /discard option to discard input sections by name (PR #189542)

[Hans Wennborg via llvm-commits]

zmodem wrote:

This basically looks good to me.

Sorry for the bikeshed but:

> For the link.exe-like interface, consider `/discard-section:`?

link.exe doesn't typically use dashses in their flags. How about `/discardSection:`?

https://github.com/llvm/llvm-project/pull/189542