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/cpptools/cpptoolsreuse.cpp

@@ -366,7 +366,6 @@ static void addBuiltinConfigs(ClangDiagnosticConfigsModel &model)
     config.setClangOptions({
         "-Wall",
         "-Wextra",
-        "-Wno-c++98-compat"
     });
     model.appendOrUpdate(config);