Question: I don't ever recall coming across anything for C that's as extensive as C++'s Boost library.

Answer: 
Depending on what exactly you're trying to do there is APR (The Apache Portable Runtime library) which is what the Apache http daemon is built on 

<http://apr.apache.org/>

For GUI, there is wxWidgets (formerly wxWindows)

<http://www.wxwidgets.org/>
Glib does compensate it partially in form of various unicode, string types. If you add Gobject you could get some object programming even some garbage collection.