[Tooling] Fix broken dependency for shared build

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()'
```

Reviewers: alexfh

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D20218

llvm-svn: 269334

1 files changed, 3 insertions, 0 deletions

diff --git a/clang/lib/Frontend/FrontendActions.cpp b/clang/lib/Frontend/FrontendActions.cpp
index c6e6a51..79c1df4 100644
--- a/clang/lib/Frontend/FrontendActions.cpp
+++ b/clang/lib/Frontend/FrontendActions.cpp
@@ -401,6 +401,9 @@ raw_pwrite_stream *GenerateModuleAction::ComputeASTConsumerArguments(
   return OS;
 }
 
+SyntaxOnlyAction::~SyntaxOnlyAction() {
+}
+
 std::unique_ptr<ASTConsumer>
 SyntaxOnlyAction::CreateASTConsumer(CompilerInstance &CI, StringRef InFile) {
   return llvm::make_unique<ASTConsumer>();