Fixing opt-asan/ubsan fail for folly contbuild

Summary: Flag caused compilation error on unused param, asserts optimized out in opt-asan/ubsan builds.  Replaced with DCHECK as per meyering's advice.

Reviewed By: meyering

Differential Revision: D5246089

fbshipit-source-id: dc0abda91f900dd98af31410f4667c52404997f5

folly/experimental/logging/LogStreamProcessor.cpp

@@ -42,7 +42,7 @@ void LogStreamProcessor::operator&(LogStream&& stream) noexcept {
   // no streaming arguments were supplied to the logging macro.
   // Therefore we don't bother calling extractMessageString(stream),
   // and just directly use message_.
-  assert(stream.empty());
+  DCHECK(stream.empty());
 
   category_->processMessage(LogMessage{
       category_, level_, filename_, lineNumber_, std::move(message_)});