[X86] Fix crash with i64 bitreverse on 32-bit targets with XOP.
    
    We unconditionally marked i64 as Custom, but did not install a
    handler in ReplaceNodeResults when i64 isn't legal type. This
    leads to ReplaceNodeResults asserting.
    
    We have two options to fix this. Only mark i64 as Custom on
    64-bit targets and let it expand to two i32 bitreverses which
    each need a VPPERM. Or the other option is to add the Custom
    handling to ReplaceNodeResults. This is what I went with.
    
    (cherry picked from commit 57c0c4a27575840ae0a48eb9f8455a5ed087c857)