vips-7.26.3 # ./configure --help
--enable-cxx build C++ components (default: test)
Also, media-gfx/nip2 does not link against libvipsCC.so, so I suggest adding a "regular" cxx USE-flag (i.e., IUSE="cxx" and not IUSE="+cxx").
In newer versions (not yet in portage), there is no longer the
configure option and the C++ dependency seems to be hard.
removed from the tree