[lld] [LLD][COFF] add __{data,bss}_{start,end}__ symbols for Cygwin support (PR #136180)

[Martin Storsjö via llvm-commits]

https://github.com/mstorsjo commented:

This looks reasonable, but would need some sort of test; have a look in `lld/test/COFF` for something to use as model.

https://github.com/llvm/llvm-project/pull/136180