OverloadCandidateSet: Stop exposing SmallVector internals

Replace push_back with addCandidate which will let us make use of the fixed size of
the conversion sequence vector soon.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@148185 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed