[clang] [clang-tools-extra] [compiler-rt] [flang] [lld] [lldb] [llvm] [mlir] [openmp] Treewide C++26/2d fixes (PR #223284)

[Aaron Ballman via llvm-commits]

AaronBallman wrote:

> To be clear, I don't suggest that LLVM itself start using C++26 features, just that code be written in the relatively large intersection between C++17 and C++26 so that out-of-tree consumers are not being limited.

I'm aware of that goal, but I'm not convinced the code is cleaner or easier to maintain with the changes, at least in all cases (I'm also a bit wary of the number of places we're now explicitly creating a `Twine` to work around the standard breaking working code by adding new overload sets). We might want to even split based on the kind of fix (so we're fixing all of the `Twine` in one component in one PR, etc). By splitting it up, we can hopefully make progress on changes that are less contentious while debating what to do about other changes, but it also makes it more likely we spot issues with the changes. They're meant to be NFC, but it's hard to motivate reviewers to look at 118 changed files in any amount of detail.

https://github.com/llvm/llvm-project/pull/223284