qtbase doesn't build with latest clang

When trying to build qtbase stable (5.1.1., 37351bbe) with clang (svn r185149) under Linux, we get compile errors even when building qmake:

/p/qtbase/include/QtCore/../../src/corelib/io/qurl.h:327:31: error: friend declaration specifying a default argument must be a definition
    friend Q_CORE_EXPORT uint qHash(const QUrl &url, uint seed = 0) Q_DECL_NOTHROW;
                              ^
1 error generated.

According to N3337 it seems the compiler is right, cf. §8.3.6.4 [dcl.fct.default] "If a friend declaration specifies a default argument expression, that declaration shall be a definition and shall be the only declaration of the function or function template in the translation unit."