When updating or installing, compilation fails, either with CLANG or GCC. Setting DISABLE_MAKE_JOBS in /etc/make.conf doesn't solve the problem as expected. See below error message with DISABLE_MAKE_JOBS set.

[...]
[ 13%] Built target processui_automoc
[ 13%] Generating ui_ProcessWidgetUI.h
[ 13%] Generating ui_ReniceDlgUi.h
Scanning dependencies of target processui
[ 13%] Building CXX object libs/ksysguard/processui/CMakeFiles/processui.dir/processui_automoc.o
[ 13%] Building CXX object libs/ksysguard/processui/CMakeFiles/processui.dir/ksysguardprocesslist.o
[ 13%] Building CXX object libs/ksysguard/processui/CMakeFiles/processui.dir/ProcessFilter.o
[ 13%] Building CXX object libs/ksysguard/processui/CMakeFiles/processui.dir/ProcessModel.o
/usr/ports/x11/kde4-workspace/work/kde-workspace-4.7.4/libs/ksysguard/processui/ProcessModel.cpp:424:40: error: redefinition of 'i' with a different type
        QMap<qlonglong, XID>::iterator i = mXResClientResources.lowerBound(-(qlonglong)(wid));
                                       ^
/usr/ports/x11/kde4-workspace/work/kde-workspace-4.7.4/libs/ksysguard/processui/ProcessModel.cpp:422:15: note: previous definition is here
    for (uint i=0; i < count; ++i) {
              ^
/usr/ports/x11/kde4-workspace/work/kde-workspace-4.7.4/libs/ksysguard/processui/ProcessModel.cpp:425:17: error: 'operator _Bool' is a private member of
      'QMap<long long, unsigned long>::iterator'
        if(i == mXResClientResources.end())
                ^~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/qt4/QtCore/qmap.h:294:16: note: declared private here
        inline operator bool() const { return false; }
               ^
/usr/ports/x11/kde4-workspace/work/kde-workspace-4.7.4/libs/ksysguard/processui/ProcessModel.cpp:428:15: error: member reference base type 'uint'
      (aka 'unsigned int') is not a structure or union
        if(-i.key() != (qlonglong)(wid & ~i.value()))
            ~ ^
/usr/ports/x11/kde4-workspace/work/kde-workspace-4.7.4/libs/ksysguard/processui/ProcessModel.cpp:428:45: error: member reference base type 'uint'
      (aka 'unsigned int') is not a structure or union
        if(-i.key() != (qlonglong)(wid & ~i.value()))
                                          ~ ^
/usr/ports/x11/kde4-workspace/work/kde-workspace-4.7.4/libs/ksysguard/processui/ProcessModel.cpp:441:36: error: no viable conversion from 'uint'
      (aka 'unsigned int') to 'QMap<long long, unsigned long>::iterator'
        mXResClientResources.erase(i);
                                   ^
/usr/local/include/qt4/QtCore/qmap.h:230:11: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from 'uint'
      (aka 'unsigned int') to 'const QMap<long long, unsigned long>::iterator &' for 1st argument;
    class iterator
          ^
/usr/local/include/qt4/QtCore/qmap.h:245:16: note: candidate constructor not viable: no known conversion from 'uint' (aka 'unsigned int') to
      'QMapData::Node *' for 1st argument;
        inline iterator(QMapData::Node *node) : i(node) { }
               ^
/usr/local/include/qt4/QtCore/qmap.h:378:29: note: passing argument to parameter 'it' here
    iterator erase(iterator it);
                            ^
5 errors generated.
gmake[2]: *** [libs/ksysguard/processui/CMakeFiles/processui.dir/ProcessModel.o] Error 1
gmake[1]: *** [libs/ksysguard/processui/CMakeFiles/processui.dir/all] Error 2
gmake: *** [all] Error 2
*** Error code 1

Stop in /usr/ports/x11/kde4-workspace.
*** Error code 1

Stop in /usr/ports/x11/kde4-workspace.

===>>> make failed for x11/kde4-workspace
===>>> Aborting update

===>>> Update for x11/kde4-workspace failed
===>>> Aborting update

Terminated

===>>> You can restart from the point of failure with this command line:
       portmaster <flags> x11/kde4-workspace

How-To-Repeat: Update existing x11/kde4-workspace 4.7.3 to 4.7.4 or newly install port x11/kde4-workspace.