Here's an ITPro article (obnoxiously split into six parts) comparing GCC and LLVM from a licensing point of view. "In other words GCC is constructed in such a way that those who wish to provide extensions with licences that are incompatible with the GPL and copyleft are persuaded to contribute the software back to the community in the shape of the GPL - and this has been beneficial to the community - in that it has opened up architectures and languages that might not otherwise have been available to other users of GCC."
December 17, 2010
GCC and LLVM - What's in a Licence?
Read more at LWN