[clang] [llvm] [AArch64][RISCV] Improve the tests for --print-enabled-extensions and --print-supported-extensions (PR #97829)

[Jon Roelofs via cfe-commits]

jroelofs wrote:

> The new tests are autogenerated, but I am not merging the script that creates them because there isn't a good place for it.

Mind sticking it in a gist at least so folks can use it for downstream subtargets?

https://github.com/llvm/llvm-project/pull/97829