[llvm-profdata] Use SmallSet rather that std::set for keeping track of profdata merge errors

Missed bit of feedback from D14720.

Use SmallSet<std::error_code> rather than std::set<...> in order to be more efficient.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@253474 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed