[clang] Enable descriptions for --print-supported-extensions

[cbalint13]

Enables summary descriptions along with the names of the feature.
Descriptions here are simply looked up via the available llvm tablegen data.

[DavidSpickett]

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.

[cbalint13]

@DavidSpickett

Thank you for the review time, will address all the concerns and be back with a re-review request.

[cbalint13]

@DavidSpickett ,

The new output: console-output.txt.gz

$ zcat console-output.txt.gz | grep 'print'
$ ./bin/clang --target=arm-unknown-linux-gnu --print-supported-extensions
$ ./bin/clang --target=aarch64-unknown-linux-gnu --print-supported-extensions
$ ./bin/clang --target=riscv64-unknown-linux-gnu --print-supported-extensions

Addressed all requests, let me know if still spot something.
Re-formatted the print without any '\t', but using spaces with precise justifiers.

[cbalint13]

@DavidSpickett ,

Addressed all requests.

• Here is the console output: console-output.txt.gz

$ zcat ~/console-output.txt.gz | grep 'print'
$ ./bin/clang --target=arm-unknown-linux-gnu --print-supported-extensions
$ ./bin/clang --target=aarch64-unknown-linux-gnu --print-supported-extensions
$ ./bin/clang --target=riscv64-unknown-linux-gnu --print-supported-extensions

[DavidSpickett]

Looks good to me, thanks for working on this.

I'm not sure if you'll have permissions to click the merge button but if you do, go ahead. Please remember to edit the final commit message to remove the links to the output files.

[cbalint13]

@DavidSpickett ,

Looks good to me, thanks for working on this.

Thank you very much for the time !

I'm not sure if you'll have permissions to click the merge button but if you do, go ahead.

• No, don't, I am outside contributor.

Please remember to edit the final commit message to remove the links to the output files.

• Done.

[DavidSpickett]

If you are doing more contributions you can get commit access by doing https://llvm.org/docs/DeveloperPolicy.html#obtaining-commit-access. Though with the switch to Github it's super easy to ask the reviewer to click the merge button, so it's not required.