librsvg vs librsvg-c in bulk builds

[nia <nia%NetBSD.org@localhost>]

For reference, see the following bulk build where many packages
using librsvg fail in the depends stage:

http://victory.netbsd.org/pkgsrc/packages/reports/HEAD/evbarm7-9.0/20201225.0632/meta/report.html

Example:

http://victory.netbsd.org/pkgsrc/packages/reports/HEAD/evbarm7-9.0/20201225.0632/mate-panel-1.24.1nb1/depends.log

> pkg_add: A different version of librsvg-2.40.21nb5 is already installed: librsvg-2.48.3nb3

What makes this bulk build interesting is that librsvg gets built BUT
librsvg-c is preferred, which forces an earlier version dependency:

BUILDLINK_API_DEPENDS.librsvg+= librsvg<2.41

I'd guess that this is broken due to pkg_add always preferring to
install the newer version.

Should graphics/librsvg be explicitly skipped in bulk build setups
that prefer librsvg-c? Should the PKGBASE of librsvg-c be changed
so that it's not the same as librsvg?