CppTools: set default -std=c++11 for Qt4

qmake from Qt4 does not provide C++ standard and
clang can't properly compile Qt4.8.6 and earlier
with c++1z. Behavior in this commit mimics qmake
from Qt5 which also provides c++11 as a default
standard.

Task-number: QTCREATORBUG-16441
Change-Id: I3d29891d6e47f2367f2b3b2bf4be4d86661924e9
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/cpptools/cppprojectinfogenerator.cpp

@@ -205,12 +205,15 @@ void ProjectInfoGenerator::createProjectParts(const RawProjectPart &rawProjectPa
         const ProjectPart::Ptr part = projectPartFromRawProjectPart(rawProjectPart,
                                                                     m_projectUpdateInfo.project);
 
+        ProjectPart::LanguageVersion defaultVersion = ProjectPart::LatestCxxVersion;
+        if (rawProjectPart.qtVersion == ProjectPart::Qt4_8_6AndOlder)
+            defaultVersion = ProjectPart::CXX11;
         if (cat.hasCxxSources()) {
             createProjectPart(rawProjectPart,
                               part,
                               cat.cxxSources(),
                               cat.partName("C++"),
-                              ProjectPart::LatestCxxVersion,
+                              defaultVersion,
                               ProjectPart::NoExtensions);
         }
 
@@ -219,7 +222,7 @@ void ProjectInfoGenerator::createProjectParts(const RawProjectPart &rawProjectPa
                               part,
                               cat.objcxxSources(),
                               cat.partName("Obj-C++"),
-                              ProjectPart::LatestCxxVersion,
+                              defaultVersion,
                               ProjectPart::ObjectiveCExtensions);
         }