[Tooling] Fix broken dependency for shared build

[etienneb]

Summary

There virtual destructor can't be found and cause a compilation error
on a shared build.

To repro: [Release + Shared]

-DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED_LIBS=ON

Which produce this error:

tools/clang/unittests/Tooling/CMakeFiles/ToolingTests.dir/ToolingTest.cpp.o: In function `clang::tooling::newFrontendActionFactory_CreatesFrontendActionFactoryFromType_Test::TestBody()':
ToolingTest.cpp:(.text._ZN5clang7tooling66newFrontendActionFactory_CreatesFrontendActionFactoryFromType_Test8TestBodyEv+0x49): undefined reference to `clang::SyntaxOnlyAction::~SyntaxOnlyAction()'

[etienneb]

note: To repro, you must compile the tests.

% ninja check-all

[alexfh]

LG

include/clang/Frontend/FrontendActions.h

 };
 
 class SyntaxOnlyAction : public ASTFrontendAction {
 protected:
   std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI,
                                                  StringRef InFile) override;
 
 public:
+  ~SyntaxOnlyAction() override;
   bool hasCodeCompletionSupport() const override { return true; }
 };
 
 /// \brief Dump information about the given module file, to be used for
 /// basic debugging and discovery.
 class DumpModuleInfoAction : public ASTFrontendAction {
 protected:
   std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI,

lib/Frontend/FrontendActions.cpp

raw_pwrite_stream *OS =
                           /*CreateMissingDirectories=*/true);
   if (!OS)
     return nullptr;
 
   OutputFile = CI.getFrontendOpts().OutputFile;
   return OS;
 }
 
+SyntaxOnlyAction::~SyntaxOnlyAction() {
+}
+
 std::unique_ptr<ASTConsumer>
 SyntaxOnlyAction::CreateASTConsumer(CompilerInstance &CI, StringRef InFile) {
   return llvm::make_unique<ASTConsumer>();
 }
 
 std::unique_ptr<ASTConsumer>
 DumpModuleInfoAction::CreateASTConsumer(CompilerInstance &CI,
                                         StringRef InFile) {