Clang: Fix c++98-compat warnings for MSVC toolchain

Clang invoked with --driver-mode=cl will map "-Wall" to "-Weverything",
thus enabling -Wc++98-compat-pedantic and way more options.

Fix this by escaping "-Wall" in the cl mode, effectively passing in
"/clang:-Wall" instead of "-Wall".

This fixes what 5675169e56 addressed also
for ClangTools.

Change-Id: Ideb7bab923d0359e8039b61e9d53c8765de79c29
Reviewed-by: Cristian Adam <cristian.adam@qt.io>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/clangcodemodel/clangeditordocumentprocessor.cpp

@@ -441,6 +441,7 @@ public:
     {
         // Determine the driver mode from toolchain and flags.
         m_builder.evaluateCompilerFlags();
+        m_isClMode = m_builder.isClStyle();
 
         addLanguageOptions();
         addGlobalDiagnosticOptions(); // Before addDiagnosticOptions() so users still can overwrite.
@@ -498,7 +499,10 @@ private:
                                        ? CppTools::UseBuildSystemWarnings::Yes
                                        : CppTools::UseBuildSystemWarnings::No;
 
-        m_options.append(diagnosticConfig.clangOptions());
+        const QStringList options = m_isClMode
+                                        ? CppTools::clangArgsForCl(diagnosticConfig.clangOptions())
+                                        : diagnosticConfig.clangOptions();
+        m_options.append(options);
     }
 
     void addGlobalDiagnosticOptions()
@@ -537,6 +541,7 @@ private:
     Core::Id m_diagnosticConfigId;
     CppTools::UseBuildSystemWarnings m_useBuildSystemWarnings = CppTools::UseBuildSystemWarnings::No;
     CppTools::CompilerOptionsBuilder m_builder;
+    bool m_isClMode = false;
     QStringList m_options;
 };
 } // namespace