packagedata: Show error when trying to change PE/PV/PR from runtime/pkgdata

* causes build failure before do_package_write_ipk fails when trying to use wrong WORKDIR

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
bitbake.conf: export STRINGS and GPERF

* remove exports from systemd

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
tcp-wrappers: Rename conflicting variable STRINGS in Makefile

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
kconfig-frontends: fix building with gperf without  prefix

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
kconfig-frontends: temporary export unprefixed GPERF