[isoltest] Add support for external sources.

test/Common.h

@@ -86,4 +86,9 @@ private:
 	static std::unique_ptr<CommonOptions const> m_singleton;
 };
 
+/// @return true if it is ok to treat the file located under the specified path as a semantic test.
+/// I.e. if the test is located in the semantic test directory and is not excluded due to being a part of external sources.
+/// Note: @p _testPath can be relative but must include at least the `/test/libsolidity/semanticTests/` part
+bool isValidSemanticTestPath(boost::filesystem::path const& _testPath);
+
 }