[llvm] [NFC] Fix MSVC C4146 warnings in LLVM headers and tools (PR #225577)

[Nikita Popov via llvm-commits]

nikic wrote:

I continue to be opposed to fixing MSVC false positive warnings. Such warnings should be disabled, not mitigated.

This particular warning is not only unnecessary but also actively dangerous, because it encourages adding UB (signed integer negation has UB for signed minimum, while unsigned integer negation is always well-defined).

https://github.com/llvm/llvm-project/pull/225577