> More importantly, the "competition" between GCC and clang/LLVM is mutually beneficial. GCC losing prominence would not be good for LLVM long-term, just as GCC arguably languished in the period after the egcs merger.

You're right to note that "competition" here is more like inspiration than a deathmatch. But I vaguely remember two things that seem similar to motivation via competitive pressure to me: (1) when GCC 5 came out, it had way nicer error messages, and I immediately thought "Oh, they wanted to make GCC nice like Clang" and (2) IIRC the availability of a more modular compiler stack like LLVM/Clang essentially neutralized Stallman's old strategic argument against more a more pluggable design, right?