Seems that response from Alex was blocked by yahoogroups, so here it is:

"In 2.1 there are no changes in firebird build environment, but there
are minor changes in fbclient build process. This library is statically
linked with libstdc++ now - this makes it much better usable with other
libraries, using another versions of libstdc++. Linker used is gcc, not
g++ - in order to avoid automatically added dynamic libstdc++, at the
same time having the rest of functions linked dynamically."

Which should explain the issue, thought. I'll try to wrestle the KI
build myself as Alex is going off for 2-3 weeks starting from Monday,
but I'm not an expert and KI build system is quite scary, and I'm going
on holidays myself at the end of next week, so it's possible that you
would have to wait few weeks before this would be solved.

best regards
Pavel Cisar
IBPhoenix