[SelectionDAG] Add check for BUILD_VECTOR in isKnownNeverNaN

Includes handling of constants with vector type in isKnownNeverNaN.
For AMDGPU results in not making fcanonicalize during legalization
for vector inputs to fmaxnum_ieee and fminnum_ieee. Does not affect
end result since there is a combine that eliminates fcanonicalize.

Differential Revision: https://reviews.llvm.org/D88573