Quick build fix.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@210838 91177308-0d34-0410-b5e6-96231b3b80d8
Prefix error_code with std.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@210840 91177308-0d34-0410-b5e6-96231b3b80d8