I'm guessing the problem isn't that newer GCC lacks SPARC support, but that their (now very old and bitrotted) SPARC support relies on some kind of undefined behavior or nuance of GCC 4 that prevents newer versions from building the kernel.
I'm guessing the problem isn't that newer GCC lacks SPARC support, but that their (now very old and bitrotted) SPARC support relies on some kind of undefined behavior or nuance of GCC 4 that prevents newer versions from building the kernel.
(side tangent FWIW, NetBSD has no qualms with using GPLv3 GCC, only Free/Open do)
(Edit for another historical tangent: Sun helped create System V release 4, which specifically combined element of older SysV with BSD. Additionally, Solaris/"SunOS 5"'s predecessor SunOS 4 was a straight-up BSD. So Solaris is a pretty BSD-y UNIX, in a way...)
My point is unlike the other BSDs they haven't made a point of deprecating/removing GCC from the source tree, or even using LLVM by default where they can. For third parties worried about GPLv3, you can easily delete all GPLv3 code with a rm -rf src/external/gpl3 :)