boost-1.34.1 building multiple library variants

[Benjamin Kosnik]

This is now BZ 250802.

> It appears that the boost-1.34.1 package is building multiple library
> variants; specifically, both thread-safe and non-thread-safe versions
> of each library get built and installed.

Yes. This matches upstream behavior.

There has been some discussion of this upstream issue (see boost-build
in January, others), but no resolution. 

> This is a departure from the boost 1.33.1 package, where only the
> thread-safe variants of the libraries were built and installed.

Yes.

> Is this change deliberate? Do we really need the non-thread-safe
> variants?

This change is deliberate. The way boost is currently structured, both
are needed.
 
> This change has some unfortunate consequences. First of all, since
> there is no non-thread-safe variant of libboost_thread, there is no
> more libboost_thread.so. So someone trying to link with that library
> (which existed in the boost 1.33.1 package) will fail. But this isn't
> the worst of it. Someone linking with, for instance, -lboost_regex
> will now get a variant of the library that *is not*
> thread-safe--where with boost-1.33.1 the same -l flag links to a
> library that *is* thread-safe.

boost users expecting thread safe libraries now have to use the -mt.*
versions.

-benjamin