core/pkg-infra: Add per-package support in qmake infra

core/pkg-infra: Add per-package support in qmake infra

Qmake configured packages will, by default, use the absolute HostPrefix/Sysroot
pathes set during configuration/building of qt5base for their install
destinations.
For the per-package host/staging infrastructure, this causes non-qt5base
packages to litter the qt5base folders. In addition, buildroots target-install
step subsequently fails because the respective files are missing from the
per-package sysroot of the package itself.

Fortunately, qmake's built-in pathes can be overridden by placing a custom
qt.conf next to the qmake binary. This is already used to facilitate SDK
relocation. So for per-package path manipulation we can reuse that method, but
need to change the host/sysroot values according to each per-package
path.

Signed-off-by: Andreas Naumann <anaumann@ultratronik.de>
Reviewed-by: Yann E. MORIN <yann.morin.1998@free.fr>
[yann.morin.1998@free.fr: drop useless 'rm -f' of generated file]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>