qtbase: fix intermittent rpi-qtauto gammaray build failures
qtbase: fix intermittent rpi-qtauto gammaray build failures

With error message 'Imported target "Qt5::Gui_GLESv2" includes
non-existent path'.

Possible to reproduce before this fix by doing:

$ bitbake -c clean qtbase
$ bitbake -c configure -f gammaray

Replacing STAGING_DIR_HOST with $ENV{PKG_CONFIG_SYSROOT_DIR} seems
fragile. It is exported in poky/meta/conf/bitbake.conf though so should
always be available. Does not seem like the recipe sysroot is
propagated to CMake in any other way (some subdirs are though).

This commit can be reverted once
https://github.com/meta-qt5/meta-qt5/issues/108 is fixed upstream.

Signed-off-by: Martin Ejdestig <6245dcb10f19f01f215dad2c1bc577b6938fd827@luxoft.com>

Pelagicore/meta-pelux,Pelagicore/meta-pelux,Pelagicore/meta-pelux