Before this, if a file was installed to DESTDIR/some/dir and that directory
was missing due to not having ran 'make distrib-dirs' yet, the file would
be installed as 'some/dir'. For something like bsd.incs.mk with INCLUDEDIR
being a sub-directory of /usr/include, this could result in all of the headers
being installed to a file rather than getting a directory of them.
Now it will error that the file/directory does not exist rather than hide
the issue.
Another option being discussed is to implement GNU's install -D flag which
would auto create any missing directories.
This is a mitigation of the problem. The proper order to the build is to
run 'make distrib-dirs' first, but that can be forgotten if building from
a sub-directory after updating the source code to the latest revision.
MFC after: 2 weeks
Sponsored by: EMC / Isilon Storage Division
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