[lld] [lld][COFF] Fix: Merge `.drectve` sections in ObjFile::readSections (PR #86380)

[Martin Storsjö via llvm-commits]

https://github.com/mstorsjo commented:

Looks mostly fine to me now (i.e. no further objections from me), except for opinions on the default allocation size for the `SmallVector`.

https://github.com/llvm/llvm-project/pull/86380