devel/qmake4: "/usr/share/mk/bsd.prog.mk" line 176: Malformed conditional (${COMPILER_TYPE}

On CURRENT (FreeBSD 11.0-CURRENT #0 r265433: Tue May  6 13:37:15 CEST 2014 amd64) the
build/updating of port devel/qmake4 fails due to:

===>  Building for qt4-qmake-4.8.6
make[1]: "/usr/share/mk/bsd.prog.mk" line 176: Malformed conditional (${COMPILER_TYPE} ==
"clang" && empty(CXXFLAGS:M-stdlib=libstdc++)) make[1]: Fatal errors encountered --
cannot continue make[1]: stopped
in /usr/ports/devel/qmake4/work/qt-everywhere-opensource-src-4.8.6/qmake ===> Compilation
failed unexpectedly. Try to set MAKE_JOBS_UNSAFE=yes and rebuild before reporting the
failure to the maintainer.
*** Error code 1