that don't provide the POSIX setenv().
This fixes building plugins that link to compat.c on OS X (shared libraries on
OS X don't have direct access to environ). It also reduces the binary size on
platforms which provide setenv(), which these days is most of them.
git-svn-id: svn://svn.code.sf.net/p/bitchx/code/trunk@382 13b04d17-f746-0410-82c6-800466cd88b0