Make `promote_consts` emit the errors when required promotion fails
A very minimal version of #65942.
This will cause a generic "argument X is required to be a constant" message for `simd_shuffle` LLVM intrinsics instead of the [custom one](caa1f8d7b3/src/librustc_mir/transform/qualify_consts.rs (L1616)). It may be possible to remove this special-casing altogether after rust-lang/stdarch#825.
r? @eddyb
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