Our install page mentions operating systems and compilers we support, but doesn't mention if we support c89 or anything.

This page should be updated to mention we support c89 and any standard compliant compiler, such as ... and that we actively test on those compilers.
As the page looks now, it looks as if we only support GCC 4.1, while in reality gcc3 and any other c89 compliant compilers should work just fine.

http://api.mongodb.com/libbson/current/installing.html#supported-platforms