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

[Florian Mayer via cfe-commits]

fmayer wrote:

> > @zahiraam the default of the `ComplexRange`, `CX_None` does overflow the `2` storage bits. That means we were probably still using `CX_Full` (4 should overflow to `0`) even after #78330 (I am not sure why why that changed the default in the first place). Also it's impossible to manually choose `CX_None`.
> 
> The only valid values for the `-fcomplex-arithmetic` option are: `CX_Full`, `CX_Improved`, `CX_Promoted` and `CX_Basic`. Using `clang.exe -fcomplex-arithmetic=none t.c` would lead to this error: `clang: error: unsupported argument 'none' to option '-fcomplex-arithmetic='` So `2` bits of storage is enough for `ComplexRange`. `ComplexRange` values can only be 4 values above. The value `CX_None` is the defaut value given to the `Range` when no `fcomplex-arithmetic` is used on the command line. https://github.com/llvm/llvm-project/blob/main/clang/lib/Driver/ToolChains/Clang.cpp#L2989 but it's not a valid option for `fcomplex-arithmetic`.

Then why does this assertion trigger if I don't pass anything?

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