[llvm] [MC][X86] Set SHF_X86_64_LARGE on mergeable constant sections for large code-model (PR #190903)

[Farid Zakaria via llvm-commits]

fzakaria wrote:

@aeubanks okay I added more diagnostics -- turns out I induced it with a change internally.... oops :P
Moving constants to .lrodata.cst* happened to sidestep the buggy code path, which is why I initially attributed the fix to this change.

That said, this PR is still correct on its own merits: #81900 fixed named globals to use .lrodata.cst* with SHF_X86_64_LARGE
via the CodeGen path, but left the MC path (initELFMCObjectFileInfo) hardcoded to .rodata.cst*. This follows up the work #81900 started. 

I still think it's a good change /shrug but if we disagree will close.

https://github.com/llvm/llvm-project/pull/190903