ThreadSafetyReporter: Manage diagnostics in a std::list.

std::list is expensive, but so is std::sorting a SmallVector of SmallVectors of
heavyweight PartialDiagnostics.

Saves ~30k in a i386-linux-Release+Asserts clang build.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@153437 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed