qtserialport fails to build with Qt5 under Mac OS X

I attempted to build qtserialport using Qt5 beta on a Macintosh and got the following error:

david-betzs-macbook-pro:parallax dbetz$ mkdir qtserialport-build
david-betzs-macbook-pro:parallax dbetz$ cd qtserialport-build
david-betzs-macbook-pro:qtserialport-build dbetz$ qmake ../qtserialport/serialport.pro
david-betzs-macbook-pro:qtserialport-build dbetz$ make
cd src/ && ( test -f Makefile || /Users/dbetz/work/qt5/qtbase/bin/qmake /Users/dbetz/Dropbox/parallax/qtserialport/src/src.pro -o Makefile ) && make -f Makefile
Project MESSAGE: /Users/dbetz/work/qt5/qtbase/bin/syncqt -check-includes -module -mkspecsdir /Users/dbetz/work/qt5/qtbase/mkspecs -outdir /Users/dbetz/work/qt5/qtbase /Users/dbetz/Dropbox/parallax/qtserialport
<srcbase> = /Users/dbetz/Dropbox/parallax/qtserialport
<outbase> = /Users/dbetz/work/qt5/qtbase
No such module: -mkspecsdir at /Users/dbetz/work/qt5/qtbase/bin/syncqt line 803.
Project ERROR: Failed to run: /Users/dbetz/work/qt5/qtbase/bin/syncqt -check-includes -module -mkspecsdir /Users/dbetz/work/qt5/qtbase/mkspecs -outdir /Users/dbetz/work/qt5/qtbase /Users/dbetz/Dropbox/parallax/qtserialport
make: *** [sub-src-make_first-ordered] Error 3