Lower FNEG just like FABS to fneg[ds] and fmov[ds], thus avoiding
expensive libcall. Also, Qp_neg is not implemented on at least
FreeBSD. This is also what gcc is doing.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202422 91177308-0d34-0410-b5e6-96231b3b80d8