[clang] [clang] Allow extra semicolons inside classes also in C++ pedantic mode. (PR #172209)

[via cfe-commits]

Sirraide wrote:

> If I remove the compatibility warnings and instead use a non-extension warning under `-Wextra-semi`, how should I handle the diagnostic groups for `-Wc++11-extra-semi` and `-Wc++98-compat-extra-semi`? Would they remain as groups, but unused by any diagnostic?

Can we alias those diagnostic groups to `-Wextra-semi`? I feel like they might still be useful for people who try to be compatible w/ older compilers (where this hasn’t been backported)

https://github.com/llvm/llvm-project/pull/172209