[llvm] [X86][GlobalIsel] G_BITCAST support (PR #144473)

[Evgenii Kudriashov via llvm-commits]

e-kud wrote:

> > @mahesh-attarde could you please elaborate why this change is needed because the tests pass without this PR: https://godbolt.org/z/EEzP4nn4n
> > There is a problem with double conversions in `test2` on `i686` but it is all over there.
> 
> While doing FP class test we need to convert F32 to I32 and F64 to I64 and create sequence of bitwise ops.

Is there a test in IR or GIR that shows the problem? Because current tests only show that this PR workarounds an issue with doubles on `i686`.

https://github.com/llvm/llvm-project/pull/144473