Frontend: Fix memory leak in CompilerInstance::setVerboseOutputStream

Found this memory leak in `CompilerInstance::setVerboseOutputStream` by
inspection; it looks like this wasn't previously exercised, since it was
never called twice.

Differential Revision: https://reviews.llvm.org/D93249

Author: dexonsmith

clang/lib/Frontend/CompilerInstance.cpp

@@ -85,7 +85,7 @@ void CompilerInstance::setDiagnostics(DiagnosticsEngine *Value) {
 }
 
 void CompilerInstance::setVerboseOutputStream(raw_ostream &Value) {
-  OwnedVerboseOutputStream.release();
+  OwnedVerboseOutputStream.reset();
   VerboseOutputStream = &Value;
 }
 

clang/unittests/Frontend/OutputStreamTest.cpp

@@ -101,4 +101,12 @@ TEST(FrontendOutputTests, TestVerboseOutputStreamOwned) {
   EXPECT_TRUE(StringRef(VerboseBuffer.data()).contains("errors generated"));
 }
 
+TEST(FrontendOutputTests, TestVerboseOutputStreamOwnedNotLeaked) {
+  CompilerInstance Compiler;
+  Compiler.setVerboseOutputStream(std::make_unique<raw_null_ostream>());
+
+  // Trust leak sanitizer bots to catch a leak here.
+  Compiler.setVerboseOutputStream(llvm::nulls());
+}
+
 } // anonymous namespace