[llvm] [IR] Use EXPORTAS for ARM64EC mangled symbols with dllexport attribute. (PR #81940)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

I'm a bit concerned about the interaction between emitLinkerFlagsForGlobalCOFF() and the EC lowering pass.

It looks like emitLinkerFlagsForGlobalCOFF() is used by LTO to compute this data in some (?) cases.  This is before we'd normally do EC lowering.  But the code generator calls it late, after EC lowering.  So there's going to be some inconsistency there.

That said, I'm not really sure what the linker is actually doing with the flags before LTO.  And I guess supporting LTO isn't really a high priority at the moment.  Maybe worth leaving a FIXME, at least.

https://github.com/llvm/llvm-project/pull/81940