PATCH: Support libtool -no-undefined under GNU/Linux (also *BSD, other GNU ld systems)

[Loren James Rittle]

> Anyhow, for anyone who (still) cares, attached are unidiffs to vanilla 
> libtool 1.5 that implement libtool's -no-undefined option on GNU/Linux 
> and other platforms that use GNU ld (e.g. *BSD variants, although I've 
> only tested on Linux and FreeBSD 4.8).

> I needed to add a -pthread flag so that on *BSD libtool could decide 
> whether to add a dependency on -lc_r (to resolve undefined symbols) or 
> just turn off the undefined symbol checking.  While this does defeat the 
> checking in the common case, that seemed preferable to creating shared 
> libraries/modules that broke threaded applications.  I figured that any 
> application built with -pthread probably uses the extra functions in 
> -lc_r, so adding a dependency there wasn't likely to break anything.

FYI, FreeBSD 5.0 has different rules about -lc and -lc_r than
FreeBSD 4 (in 5, both appear instead of -lc_r replacing -lc).

Regards,
Loren