default searchpaths on *BSD machines?

[Miles Bader]

I notice that FreeBSD (etc) put a lot of optionally installed
("/usr/ports") software in /usr/local, but the system compiler's
search-paths on these machines by default _don't_ include
/usr/local...

So my autoconf'd project doesn't find various libraries, even if the
user thought he had installed them.

What's the usual way to handle this issue...?

  1) Add /usr/local to paths by default
  (e.g. CPPFLAGS+=-I/usr/local/include, LDFLAGS+=-L/usr/local/lib)

  2) Add $(prefix) to paths by default

  3) Somehow detect such a system, and do one of the above only for
  them...

  4) Have an option to set this (--with-extra-seach-root= ... argh ugly
  name but), but require the user give the option explicitly

  5) Insist the user specify CPPFLAGS, LDFLAGS, etc, on the configure
  command-line

  6) ...?

[Do FreeBSD Makefiles set things up to search /usr/local by default?]

Thanks,

-Miles

-- 
Learning, n. The kind of ignorance distinguishing the studious.