Once again, Gcc and its lack of modularity has been raised as an issue and contrasted with LLVm, the new compiler on the block. GCC is huge and venerable: 5 million lines, 30 years, and growing. LLVM, in contrast, is relatively youthful and modular and allows free and proprietary languages to be added as modules.
The core of LLVM is ‘open source’. GCC is copyleft and unreservedly free software and doesn’t allow plug-ins or other means to add proprietary extensions to the GCC code.