[clang] [clang] Add -Wimplicit-fallthrough to -Wextra (PR #97926)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> @AaronBallman sure. Should I still use http://llvm-compile-time-tracker.com/ , or do I run the benchmark another way?

Sorry, your question completely fell off my radar! llvm-compile-time-tracker would be fine, but even just a local test would suffice -- basically, I expect the test case from #105959 to be slow before you apply your patch and am just wondering whether that gets even slower with your patch.

https://github.com/llvm/llvm-project/pull/97926