[clang] [clang][driver] Improve warning message for complex range overrides and GCC incompatibility (PR #149028)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> @andykaylor @AaronBallman What do you think about making the warnings about complex range behave as described above? Any feedback would be greatly appreciated.

CC @zahiraam @jcranmer-intel for additional opinion

My first thought is that this is an improvement, but the design space is complicated enough I'd like to hear from folks with more experience in case I'm missing something. (I wonder whether omnibus options like `-ffast-math` also complicate things?)

https://github.com/llvm/llvm-project/pull/149028