[clang] [clang] Assert the enum FPOpts and LangOpts fit into the storage (PR #126166)

[Jan Svoboda via cfe-commits]

jansvoboda11 wrote:

The idea here makes sense to me and I don't mind if it lands without "NFC" in the title, but I think enforcing this at compile time would be more robust. Could we use `static_assert` with something like `llvm::BitWidth` and supporting infrastructure from `llvm/include/ADT/BitmaskEnum.h`?

https://github.com/llvm/llvm-project/pull/126166