Log Message:
x11/qt5-qtbase: add QMAKE_STRIP to pkgsrc qmake.conf.

In upstream qmake, QMAKE_STRIP is defined in places such as
common/bsd/bsd.conf and common/linux.conf. The pkgsrc version of
qmake.conf includes none of those. So add it there.
For the special mac version, just include bsd/bsd.conf.

The missing name was discovered while updating x11/XaoS.