pkgbase: put library links and symlinks in the -dev package

[dfr]

Summary

Some libraries (e.g. ncurses) install links to the main library for
backwards compatibilty. This change ensures that those links are in the
dev package since the files being linked to are in that package.

PR: 249143
MFC after: 1 week

Test Plan

Run 'make packages', manually inspect packages to see that the symlinks are in the correct package.

[emaste]

I wonder if something like LINKTAGS=dev and then

.if defined(LINKTAGS)
        ${INSTALL_LINK} ${TAG_ARGS:D${TAG_ARGS},${LINKTAGS}} ${DESTDIR}${s} ${DESTDIR}${t}

is more clear?

[dfr]

In D41841#953640, @emaste wrote:

I wonder if something like LINKTAGS=dev and then

.if defined(LINKTAGS)
        ${INSTALL_LINK} ${TAG_ARGS:D${TAG_ARGS},${LINKTAGS}} ${DESTDIR}${s} ${DESTDIR}${t}

is more clear?

I like it - I'll make that change and update the diff.

[dfr]

Use a new variable, LINKTAGS, to make the interface between bsd.lib.mk and bsd.links.mk clearer.