ARM: use the proper target object format for WoA

WoA uses COFF, not ELF.  ARMISelLowering::createTLOF would previously return ELF
for any non-MachO platform.  This was a missed site when the original change for
target format support for Windows on ARM was done.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209057 91177308-0d34-0410-b5e6-96231b3b80d8