[clang] [lld] [llvm] [Windows] Add support for emitting PGO/LTO magic strings in the Windows PE debug directory (PR #114260)

[Alexandre Ganea via cfe-commits]

aganea wrote:

I had a more in-depth look at this. Overall I don't agree with the whole direction of this patch. I don't think it's wise for LLD to emit debug records/`coffgrp` that do not match what MSVC is generating. We can't just blindly emit a record with the string of the debug type (ie. PGI/PGU/LTCG). These strings are headers for opaque/undocumented structures that Microsoft is generating for its tooling (debugger).  Unless we're willing to understand and document those structures, so that LLD can emit them proper, I wouldn't emit these `coffgrp` at all. Also as a reference: https://www.hexacorn.com/blog/2015/07/30/gctl-debug-section-in-windows-10-binaries/

https://github.com/llvm/llvm-project/pull/114260