Fix data layout mismatch between LLVM and Clang for i686-pc-windows-msvc-elf

Do the same thing as win64. If we're not using COFF, use the ELF
manglings. Maybe if we are targetting *-windows-msvc-macho, we should
use darwin manglings, but I don't need to stir that pot today.

llvm-svn: 233819