[llvm] [X86][GlobalIsel] Support G_IS_FPCLASS (PR #162232)

[via llvm-commits]

mahesh-attarde wrote:

> Current generic lowering differs from SDAG in two ways.
> 
> 1. X86 DAG uses signed comparisons where as X86 Generic GISEL adds unsigned compares.
> 2. Sequence like `xor ecx ecx; or cl, al` is not combined in GISEL.
Missing Optimization issue https://github.com/llvm/llvm-project/issues/162248

https://github.com/llvm/llvm-project/pull/162232