Clang: Avoid warnings about unknown warning options

...as they are generated by e.g. Q_OBJECT use.

Previously we have avoided Q_OBJECT warnings by using
-Wno-unknown-pragmas (Qt Creator build with libclang 3.9). With the
upgrade to libclang 5.0 GCC pragmas can now be parsed by clang and the
related warning option thus changed to -Wunknown-warning-option.

Note that previously -Wno-unknown-pragmas was part of every built-in
configuration and visible in the UI. Now that option and the new one are
added behind the scenes (not visible in the UI anymore) so that every
diagnostic configuration, also the copied/customized ones, will profit
from it. Still, by putting this hidden options first on the command
line, the user can overwrite them with his own configuration if desired.

Task-number: QTCREATORBUG-17460
Change-Id: I68aaec1b4791522bd8dc4e5fdb405cc5b9c9f514
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/plugins/clangcodemodel/clangeditordocumentprocessor.cpp

@@ -439,6 +439,7 @@ public:
         , m_projectPart(projectPart)
     {
         addLanguageOptions();
+        addGlobalDiagnosticOptions(); // Before addDiagnosticOptions() so users still can overwrite.
         addDiagnosticOptions();
         addGlobalOptions();
         addPrecompiledHeaderOptions();
@@ -519,6 +520,15 @@ private:
         addXclangArg("-plugin-arg-clang-lazy", checks);
     }
 
+    void addGlobalDiagnosticOptions()
+    {
+        m_options.append({
+            // Avoid undesired warnings from e.g. Q_OBJECT
+            QStringLiteral("-Wno-unknown-pragmas"),
+            QStringLiteral("-Wno-unknown-warning-option")
+        });
+    }
+
     void addGlobalOptions()
     {
         if (!m_projectPart.project)

src/plugins/cpptools/clangdiagnosticconfigsmodel.cpp

@@ -33,11 +33,6 @@
 
 namespace CppTools {
 
-static QStringList commonWarnings()
-{
-    return { QStringLiteral("-Wno-unknown-pragmas") };
-}
-
 static void addConfigForQuestionableConstructs(ClangDiagnosticConfigsModel &model)
 {
     ClangDiagnosticConfig config;
@@ -48,7 +43,7 @@ static void addConfigForQuestionableConstructs(ClangDiagnosticConfigsModel &mode
     config.setClangOptions(QStringList{
         QStringLiteral("-Wall"),
         QStringLiteral("-Wextra"),
-    } + commonWarnings());
+    });
 
     model.appendOrUpdate(config);
 }
@@ -60,7 +55,7 @@ static void addConfigForPedanticWarnings(ClangDiagnosticConfigsModel &model)
     config.setDisplayName(QCoreApplication::translate("ClangDiagnosticConfigsModel",
                                                       "Pedantic Warnings"));
     config.setIsReadOnly(true);
-    config.setClangOptions(QStringList{QStringLiteral("-Wpedantic")} + commonWarnings());
+    config.setClangOptions(QStringList{QStringLiteral("-Wpedantic")});
 
     model.appendOrUpdate(config);
 }
@@ -86,7 +81,7 @@ static void addConfigForAlmostEveryWarning(ClangDiagnosticConfigsModel &model)
         QStringLiteral("-Wno-switch-enum"),
         QStringLiteral("-Wno-missing-prototypes"), // Not optimal for C projects.
         QStringLiteral("-Wno-used-but-marked-unused"), // e.g. QTest::qWait
-    } + commonWarnings());
+    });
 
     model.appendOrUpdate(config);
 }