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

[Andy Kaylor via cfe-commits]

andykaylor wrote:

I'm not sure the combined warning is necessary. I think just stating that the clang option overrides the GCC option is sufficient since there is no sense in which clang-specific options can be incompatible with GCC if GCC doesn't implement the option.

I think we're all in agreement that we want to consistently follow "last command wins" behavior, even when GCC doesn't. This patch isn't changing that, right?

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