Don't crash on redefinitions.

One error we were not deleting the alias or putting it in the Module. The
end result is that there was an use left of the aliasee when the module was
deleted.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208447 91177308-0d34-0410-b5e6-96231b3b80d8
Fix ARM intrinsics-overflow.ll test on Windows

Windows on ARM only supports thumb mode execution, so we have to
explicitly pick some non-Windows OS to test ARM mode codegen.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208448 91177308-0d34-0410-b5e6-96231b3b80d8