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
MC: clang-format MCAsmInfo

Apply clang-format over the header.  Reformat the docs to current LLVM style.
NFC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210633 91177308-0d34-0410-b5e6-96231b3b80d8
MC: add enumeration of WinEH data encoding

Most Windows platforms use auxiliary data for unwinding.  This information is
stored in the .pdata section.  The encoding format for the data differs between
architectures and Windows variants.  Windows MIPS and Alpha use identical
formats; Alpha64 is the same with different widths.  Windows x86_64 and Itanium
share the representation.  All Windows CE entries are identical irrespective of
the architecture.  ARMv7 (Windows [NT] on ARM) has its own format.

This enumeration will become the differentiator once the windows EH emission
infrastructure is generalised, allowing us to emit the necessary unwinding
information for Windows on ARM.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210634 91177308-0d34-0410-b5e6-96231b3b80d8
Uses generic_category instead of system_category.

Some c++ libraries (libstdc++ at least) don't seem to map to the generic
category in in the system_category's default_error_condition.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210635 91177308-0d34-0410-b5e6-96231b3b80d8
Try to fix the msvc build.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210636 91177308-0d34-0410-b5e6-96231b3b80d8