A lot (if not the majority) of GCC extensions used by Linux exist in GCC because the Linux kernel developers requested them in order to have a great level of control in terms of the generated machine code, so it's not exactly surprising that the Linux kernel relies on a lot of said GCC extensions.
Many of these extensions which the Linux kernel relies on have been added to LLVM, but obviously not all, and from the looks of it some never will, which means either Linux needs to refrain from using said extensions, or building Linux using LLVM will continue to require patching.
Many of these extensions which the Linux kernel relies on have been added to LLVM, but obviously not all, and from the looks of it some never will, which means either Linux needs to refrain from using said extensions, or building Linux using LLVM will continue to require patching.