Add some basic support for CloudABI on i686.

Some people want to experiment with building i686 CloudABI binaries. I
am not entirely sure this is a good idea, as I'd rather see Intel x32
support appear.

As it only requires a two-line change, let's at least provide compiler
to ease experimenting.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@239689 91177308-0d34-0410-b5e6-96231b3b80d8