The buildfarm has turned red aftertags/REL_13_BETA1
1858b10because VPATH builds need to use "@abs_srcdir@" and not "@abs_builddir@" for paths coming directly from the source tree. The input file of the new test got that right, but not the output file. Per complaints from several buildfarm animals, including desmoxytes and culicidae. I have also reproduced the error by myself.