[AArch64] Fix incorrect CSEL node created

[AArch64] Fix incorrect CSEL node created

Under -enable-unsafe-fp-math, SELECT_CC lowering in AArch64
transforms floating point comparisons of the form "a == 0.0 ? 0.0 : x" to
"a == 0.0 ? a : x". But it incorrectly assumes that 'x' and 'a' have
the same type which can lead to a wrong CSEL node that crashes later
due to nonsensical copies.

Differential Revision: https://reviews.llvm.org/D26394

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286231 91177308-0d34-0410-b5e6-96231b3b80d8