[clang] [clang] Enable descriptions for --print-supported-extensions (PR #66715)

[David Spickett via cfe-commits]

https://github.com/DavidSpickett requested changes to this pull request.

This looks really nice. Two overall things:

Now that ARM and AArch64 print more than just names, they should have column headers like RISC-V does. Name / Description

The clang test case `clang/test/Driver/print-supported-extensions.c` should be extended to check at least the column names and 1 row of the extension details. This is because we're now combining a few functions to produce this output, so an integration test is needed.

It is a bit ugly to have to combine these 2 sources of information but that's a larger issue that shouldn't block this.

https://github.com/llvm/llvm-project/pull/66715