build an integer and cast that to a float. This fixes a crash
caused by trying to split an f32 into two f16's.
This changes the behavior in test/CodeGen/XCore/fneg.ll because that
testcase now triggers a DAGCombine which converts the fneg into an integer
operation. If someone is interested, it's probably possible to tweak
the test to generate an actual fneg.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72162 91177308-0d34-0410-b5e6-96231b3b80d8