[llvm] [llvm] Add format check for MCSubtargetFeatures (PR #180943)

[David Spickett via llvm-commits]

DavidSpickett wrote:

> This patch adds some format check for MCSubtargetInfo class to prevent creation of inconsistent objects

I'm not sure what the correlation between some of the `// Invalid Strings` and `creation of inconsistent objects` is. Are they all strings that create unexpected objects or are some of them just defining restrictions that we haven't previously bothered to document?

And if the latter is the case, where is the documentation of that? You cited a comment in the other PR where you remove a trailing comma. Should there be changes to that comment in this PR, to be explicit what we do and do not expect?

https://github.com/llvm/llvm-project/pull/180943