Don't convert object_error's enum to and from int.

This allows the compiler to see the enum and warn about it. While in here,
fix a switch to not use a default and fix style violations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184186 91177308-0d34-0410-b5e6-96231b3b80d8