Remove windows_error.

MSVC doesn't seem to provide any is_error_code_enum enumeration for the
windows errors.

Fortunately very few places in llvm have to handle raw windows errors, so
we can just construct the corresponding error_code directly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210631 91177308-0d34-0410-b5e6-96231b3b80d8