Enable building in meta mode. This is an experimental build feature. For details see http://www.crufty.net/sjg/docs/freebsd-meta-mode.htm.
p The build is driven by dirdeps.mk using .Va DIRDEPS stored in Makefile.depend files found in each directory.
p The build can be started from anywhere, and behaves the same. The initial instance of .Xr make 1 recursively reads .Va DIRDEPS from Makefile.depend computing a graph of tree dependencies from the current origin. Setting .Va NO_DIRDEPS will skip checking dirdep dependencies and will only build in the current directory.
p As each target is made .Xr make 1 produces a meta file which is used to capture (and compare) the command line, as well as any command output. If .Xr filemon 4 is available the meta file will also capture a record of files used to produce the target by tracking syscalls.
p The build will hide commands ran unless .Va NO_SILENT is defined.
p