Evidence, not so much, but I've got anecdata, if that's any help: I used to work for a company which produced a game-playing virtual machine. We had a toolchai

Evidence, not so much, but I've got anecdata, if that's any help: I used to work for a company which produced a game-playing virtual machine. We had a toolchain that allowed building C and C++ programs for it. The toolchain was based on LLVM and gcc (because clang wasn't around at the time). Integrating gcc into our toolchain was appallingly hard, solely due to GPL restrictions. The extra work in dividing everything into GPL and non-GPL parts, interfacing between the two, producing split packaging and distribution etc was basically half a full time job. If the company had survived long enough for clang to have become stable --- which, sigh, it didn't --- we would have switched to it like a shot.