The QCC compiler is being worked on by Rob Landley, a developer with much compiler development experience that previously worked on early 64-bit TCC support. The QEMU CPU emulator has a code generator named TCG, which is short for Tiny Code Generator. The TCG generator translates code fragments from any target code supported by QEMU into a code representation that can be then executed on the host.
Using the Tiny Code Generator Interpreter (TCI) it allows running QEMU on any 32-bit or 64-bit host where as without this there is only support for the most prominent host CPU architectures. The Tiny Code Generator is part of the official QEMU release and works with x86/x86_64, ARM, MIPS, PowerPC, and other emulated environments.
The goal of QCC is to leverage QEMU's Tiny Code Generator/Interpreter rather than having to rewrite target code for all of these different architectures. The Tiny C Compiler right now just supports x86/x86_64 and some ARM support. It's certainly an interesting concept especially with QEMU working well already on most platforms and the TCC fork not having a huge development base.
Information on QCC can be found on Landley's home-page but there isn't too much information or code available right now as he's engaged on other projects too. QEMU's code generator is outlined on the QEMU Wiki.