Created attachment 232475 [details] Patch that fixes the issue. The build(7) manpage, in the third paragraph ("A source tree...") refers to MAKEOBJDIRPREFIX as an "environment variable". Later, in the descriptions of the "buildworld" and "buildkernel" targets, MAKEOBJDIRPREFIX is referred to as a make(1) variable. Further down, MAKEOBJDIRPREFIX is listed in the "ENVIRONMENT" section, thus making me suspect it should be always referred to as an environment variable. The patch fixes the above issue.
Keyword: patch or patch-ready – in lieu of summary line prefix: [patch] * bulk change for the keyword * summary lines may be edited manually (not in bulk). Keyword descriptions and search interface: <https://bugs.freebsd.org/bugzilla/describekeywords.cgi>