[LoopInterchange] Support loop interchange with floating point reductions

Enabled loop interchange support for floating point reductions
if it is allowed to reorder floating point operations.

Previously when we encouter a floating point PHI node in the
outer loop exit block, we bailed out since we could not detect
floating point reductions in the early days. Now we remove this
limiation since we are able to detect floating point reductions.

Reviewed By: #loopoptwg, Meinersbur

Differential Revision: https://reviews.llvm.org/D117450