[lld] [LLD][COFF] Use EC symbol table for exports defined in module definition files (PR #123849)

[Jacek Caban via llvm-commits]

cjacek wrote:

I experimented with something similar in an earlier version of ARM64X support, where I called it `COFFNamespace`, see https://github.com/cjacek/llvm-project/commit/de3b8481eeaa0af92c041c9b9a7c987e10395821#diff-e0126077b0ef020c4220f67717f0c3a7040f30473484ef2a2e702a5daddb42ab. At that time, I didn't move functions to that class and instead stored the symbol table inside it rather than using inheritance, which made it feel like an unnecessary complication. Your suggested approach seems good, I’ll revisit it.

https://github.com/llvm/llvm-project/pull/123849