[llvm] GlobalISel/Combiner: Fix building G_CONSTANT for fp extended LLT (PR #196397)

[Petar Avramovic via llvm-commits]

petar-avramovic wrote:

I just try to have types that can be selected by instruction select

the 
>       .legalFor({p0, s8, s16, s32, s64})
part is fine, it is ok to check for s32 because i32 is s32

but the problem is that inst-select only accepts i32
so I need to 
> .clampScalar(0, i8, i64);

Before inst select, most of the instructions need to use i32 explicitly. Think we can get away with some being s32 but it is very few.

https://github.com/llvm/llvm-project/pull/196397