[X86][FastISel] Fix lowering of overflow result on AVX512 targets

[X86][FastISel] Fix lowering of overflow result on AVX512 targets

    Summary:
    Fix a case where the overflow value of type i1, which is legal on AVX512, was assigned to a VK1 register class.
    We always want this value to be assigned to a GPR since the overflow return value is lowered to a SETO instruction.

    Fixes pr30981.

    Reviewers: mkuper, igorb, craig.topper, guyblank, qcolombet

    Subscribers: qcolombet, llvm-commits

    Differential Revision: https://reviews.llvm.org/D26620

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286958 91177308-0d34-0410-b5e6-96231b3b80d8