Use generic_category from the std namespace.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210736 91177308-0d34-0410-b5e6-96231b3b80d8
Driver: use more range-based for loops

Mechanical change converting some of the simpler for loops into range-based for
loops.  NFC.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210738 91177308-0d34-0410-b5e6-96231b3b80d8
Give clang-format its own error category.

The posix errno values are probably to the best thing to use for
describing parse errors.

This should also fix the mingw build.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210739 91177308-0d34-0410-b5e6-96231b3b80d8