Support: correct Windows normalisation

If the environment is unknown and no object file is provided, then assume an
"MSVC" environment, otherwise, set the environment to the object file format.

In the case that we have a known environment but a non-native file format for
Windows (COFF) which is used for MCJIT, then append the custom file format to
the triple as an additional component.

This fixes the MCJIT tests on Windows.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205130 91177308-0d34-0410-b5e6-96231b3b80d8
ARM64: override all the things.

Actually, mostly only those in the top-level directory that already
had a "virtual" attached. But it's the thought that counts and it's
been a long day.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205131 91177308-0d34-0410-b5e6-96231b3b80d8
ARM64: remove -m32/-m64 mapping with ARM.

This is causing the ARM build-bots to fail since they only include
the ARM backend and can't create an ARM64 target.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205132 91177308-0d34-0410-b5e6-96231b3b80d8
ARM64: remove unused variables

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205133 91177308-0d34-0410-b5e6-96231b3b80d8