[llvm] [RISCV] Assert extensions are sorted at compile time. NFCI (PR #77442)

[Luke Lau via llvm-commits]

lukel97 wrote:

> I have a slight concern that one of the compilers that LLVM is meant to be buildable by is unhappy with the use of `constexpr`. Sadly MSVC 16.7 (apparently the [oldest supported version](https://llvm.org/docs/GettingStarted.html#check-here)) doesn't seem to be available on godbolt though :/

Yes, we ran into some MSVC specific issues before in https://github.com/llvm/llvm-project/pull/66199, where the constexpr was too complicated and exceeded a step limit.
The windows CI seems to have fallen over for some MLIR related build failure, so I've just restarted it there. But it looks to be using MSVC 16.11?

https://github.com/llvm/llvm-project/pull/77442