Building applications which use QtDBus fails when QT_NO_CAST_FROM_ASCII is defined and clang is used

Commit 5be6cf0a6e306ed3a51ed5ba89317b1317544eea changed the signature of QDBusServer's constructor from `const QString &address, QObject *parent = 0)' to `const QString &address = "unix:tmpdir=/tmp", QObject *parent = 0)'.

When some code #includes <QtDBus/QtDBus>, which in turn ends up including qdbusserver.h, clang fails to compile the code with the following error message:

In file included from /usr/home/rakuco/kde4/qt4/include/QtDBus/QtDBus:19:
/usr/home/rakuco/kde4/qt4/include/QtDBus/qdbusserver.h:64:42: error: calling a private constructor of class 'QString'
QDBusServer(const QString &address = "unix:tmpdir=/tmp", QObject *parent = 0);
^
/usr/home/rakuco/kde4/qt4/include/QtCore/qstring.h:597:5: note: declared private here
QString(const char *ch);
^
1 error generated.

This is FreeBSD's clang:
% clang --version
FreeBSD clang version 3.0 (branches/release_30 142614) 20111021
Target: x86_64-unknown-freebsd9.0
Thread model: posix

Building the attached testcase with a recent enough version of clang should trigger the problem.