don't match on the spec name in qconfig.pri

don't match on the spec name in qconfig.pri

this will fail now even on unix (and wouldn't have ever worked on
windows), as the full spec name is known only after reading the spec,
and qconfig.pri is read from inside the spec.
matching on the host_build flag is cleaner anyway.

Change-Id: I7da144e89ab3db0fad942d755d8cb0a0f3b85588
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Donald Carr <sirspudd@gmail.com>
Reviewed-by: Girish Ramakrishnan <girish.1.ramakrishnan@nokia.com>