Out of tree build no longer possible

The pytests are expected toplevel:

 make -f ../Makefile -C build VPATH=.. ARCHIVE=osinfo-db.tar.xz

works but

make -f ../Makefile -C build VPATH=.. ARCHIVE=osinfo-db.tar.xz check

fails like

$ make -f ../Makefile -C build VPATH=.. ARCHIVE=osinfo-db.tar.xz check
make: Entering directory '/var/scratch/src/libosinfo/osinfo-db/build'
python3 -m pytest
=============================================================================================== test session starts ===============================================================================================
platform linux -- Python 3.7.3rc1, pytest-3.10.1, py-1.7.0, pluggy-0.8.0
hypothesis profile 'default' -> database=DirectoryBasedExampleDatabase('/var/scratch/src/libosinfo/osinfo-db/build/.hypothesis/examples')
rootdir: /var/scratch/src/libosinfo/osinfo-db/build, inifile:
plugins: hypothesis-3.71.11, celery-4.2.1
collected 0 items                                                                                                                                                                                                 

========================================================================================== no tests ran in 0.21 seconds ===========================================================================================
make: *** [../Makefile:124: check] Error 5
make: Leaving directory '/var/scratch/src/libosinfo/osinfo-db/build'

If one hacks around this (by ln -s build/test ../test this break due to the tests looking at the .in files instead of the data generated by the build.