[PATCH] Don't build libzgcj all the time

[DJ Delorie]

> Absolutely.  The general case I had in mind was an n-by-n dependancy
> matrix of "possible things we build" versus "things that they need".
> The Java compiler and libz, the C++ compiler and libstdc++, etc.

All I meant was some generic "extra_target_libs" that's built based on
other config options.  We'd add zlib if java was enabled, libstdc++ if
C++ is enabled, etc.  IIRC, your patch had a $target_zlib variable,
which isn't very generic.