built-in libarchive

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

If a platform provides libarchive, pkgsrc will correctly use it
rather than archivers/libarchive. If a package is silly enough to use
PKG_CHECK_MODULES instead of AC_CHECK_LIBS (unfortunately there is a
lot of it about), the libarchive provided by NetBSD won't be found. I
tried fiddling src/external/bsd/libarchive/lib/libarchive/Makefile to
generate and install a /usr/lib/pkgconfig/libarchive.pc file, but it
seems that pkgsrc doesn't look in /usr/lib/pkgconfig. Any thoughts on
what The Right Way is?

Cheers,

Patrick