Fixed resolution of QMAKESPEC on Windows.

Fixed resolution of QMAKESPEC on Windows.

base_vars["QMAKESPEC_ORIGINAL"] is not guaranteed to be set the first
time resolveSpec is called, since an include() can wipe it out.  Change
it so that resolveSpec is called repeatedly until some
QMAKESPEC_ORIGINAL is set.

The code which attempted to remove all of the path up to the last / was
incorrect and must have been dead code (or its wrongness didn't matter)
until now.

Change-Id: I2b31ae10fc284ac7293c3cd95e5a2fd503ca7ab0
Reviewed-by: Marius Storm-Olsen <marius.storm-olsen@nokia.com>