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

[Jonathan Thackray via cfe-commits]

https://github.com/jthackray approved this pull request.

Large diff! LGTM, although obvs haven't read every line :)

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