[clang] [clang][driver] Fix -print-target-triple OS version for apple targets (PR #104037)

[Louis Dionne via cfe-commits]

ldionne wrote:

@mstorsjo I think you put the finger on something I don't really understand at the moment. What is the relationship between `armv7` and `thumbv7` as a target triple? Is there any documentation on what an "effective triple" is in comparison to a "non-effective triple"?

Separately from this, we noticed that `clang -target armv7k-apple-watchos` would pass `-target thumbv7-apple-watchos` to the frontend, but using `clang -target thumbv7-apple-watchos` directly in the driver doesn't work. Is `thumbv7-apple-watchos` the "effective" triple of `armv7k-apple-watchos`? Why do both spellings exist, and what is each spelling used for?

I know that's a lot of questions, but if you know the answer to any of them, it would shed a lot of light over here :)

https://github.com/llvm/llvm-project/pull/104037