Bug#1125140: vtk9: build docs in arch-independent build only

[Drew Parsons]

Package: vtk9
Version: 9.5.2+dfsg2-4
Severity: normal

The vtk source package has been configured to build docs using doxygen.

The main problem is that doxygen is not available on all arches (it's
missing on the unofficial arches), and therefore vtk9 is unable to
build on these less common architectures.

It should be possible to reconfigure the build so that the doc build
is only made for an arch-independent build.

This would allow vtk9 to become available on all arches,
and might have the side effect of speeding up the build on the common
architectures since the doc build would not be needed for their
arch-binary builds.

It would involve
  Build-Depends-Indep: doxygen
to keep doxygen from blocking the vtk9  build on the less common architectures.