Proposal to make better use of 5th arg to AC_CHECK_LIB and AC_SEARCH_LIBS

[Steven G. Johnson]

Rainer wrote:
> * If this first attempt fails, a second attempt should be made with
>   *both* -lhesiod and -lresolv on the link line.  If this succeeds, both
>   -lhesiod and -lresolv should be added to LIBS.

I think that the 5th argument of AC_CHECK_LIB is intended primarily for
the case where you *don't* want the auxiliary libraries to be added to
LIBS, since they're going in your own private variable (e.g. @X_LIBS@)
that you'll add to the link command separately.

(Usually, in this case, you'll also override ACTION-IF-FOUND to not put
the result in LIBS either.)

> * It always tries to use -lresolv, while it may be necessary (or even
>   present) only on some platforms.  This may even be harmful in some
>   cases:

This kind of pathology is best encapsulated in a separate check, I
think.  i.e. you have a check (or a macro) that detects whether -lresolve
is present/working, and sets RESOLVE_LIB appropriately.  Then, if you
want, you can either add $RESOLVE_LIB to $LIBS, or use it in the 5th
argument of AC_CHECK_LIB if you don't want it in $LIBS.

Steven