[lld] [LLD][COFF] Support ARM64EC in BitcodeFile::getMachineType (PR #115474)

[Jacek Caban via llvm-commits]

cjacek wrote:

This patch introduces initial support for LTO on ARM64EC. It seems to work fine for simple cases, but I haven’t yet addressed full support. One issue is symbol mangling: currently, the bitcode files contain demangled symbol names, which get mangled during compilation. We might need to anticipate this mangling and adjust for it in `BitcodeFile::parse`, similar to how we create anti-dependency symbols for x86_64 object files.

Additionally, on ARM64EC, we can have a mix of x86_64 and ARM64EC bitcode files. At the moment, this will emit a warning and attempt to interpret one bitcode format as the other. We should probably handle this by splitting it into two separate compilations.

https://github.com/llvm/llvm-project/pull/115474