[compiler-rt] Fix __isOSVersionAtLeast for Android (PR #80496)

[Dan Albert via llvm-commits]

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

Discussed over IM. Not a regression because the problem I'm worried about `__builtin_available` returning true when it should not) already exists with an N+1 preview when using `__builtin_available(android 10000)`. That's probably going to be something we have to deal with eventually, but I don't think we _can_ deal with that here until the OS gives us clearer signals.

https://github.com/llvm/llvm-project/pull/80496