bsd.man.mk: Add a MANSRC.{TARGET} variable

[jhb]

Summary

This can be used to specify an alternate source file name for an
individual manpage. For example, the following snippet:

MAN=   foo::bar.3
MANSRC.foo::bar.3= foo__bar.3

Will install a foo::bar.3 manpage but use foo__bar.3 as the source
input to MANFILTER, etc.

Suggested by: ivy
Sponsored by: Chelsio Communications

[jhb]

share/mk/bsd.man.mk

241

This dependency is just odd and seems wrong.

Many of our install targets do not have any dependency at all so as to avoid building things during make install. Those that do have dependencies depend on the thing being installed, not the _source_ of the thing being installed as is done here. For now I've preserved existing behavior.

Humm, I tracked down the commit that added the weird dependency to a bde@ commit: rGeb89687138bfc3ed337544ea6e29a37931dc8f16

[ivy]

share/mk/bsd.man.mk

241

i think if we're changing this anyway, this would be a good chance to fix this. does a clean build work without this dependency?

[jhb]

share/mk/bsd.man.mk

241

Well, I would rather remove this in a separate commit I think. That said, I think bde@'s edge case isn't part of a normal clean build, it's only when you use NOMANCOMPRESS (maybe WITHOUT_MANCOMPRESS=yes now).