ClangCodeModel: Add test for "follow symbol"

These are the tests from clangbackend, so we are now up to par coverage-
wise.

Change-Id: I7b8a63109bff17745782a646f684fd795f732672
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangcodemodel/clangutils.h

@@ -78,7 +78,7 @@ public:
     QString error;
 };
 
-enum CompilationDbPurpose { Project, CodeModel };
+enum class CompilationDbPurpose { Project, CodeModel };
 GenerateCompilationDbResult generateCompilationDB(CppTools::ProjectInfo projectInfo,
                                                   CompilationDbPurpose purpose);