Work around an MSVC2017 update 3 codegen bug.

C2017 update 3 produces a clang that crashes when compiling clang. Disabling
optimizations for StmtProfiler::VisitCXXOperatorCallExpr() makes the crash go
away.

Patch from Bruce Dawson <brucedawson@chromium.org>!
https://reviews.llvm.org/D35757

llvm-svn: 308897