Support: generalise object type handling for Windows

This generalises the object file type parsing to all Windows environments.  This
is used by cygwin as well as MSVC environments for MCJIT.  This also makes the
triple more similar to Chandler's suggestion of a separate field for the object
file format.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205219 91177308-0d34-0410-b5e6-96231b3b80d8