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

[Dan Albert via llvm-commits]

DanAlbert wrote:

But a preview of N+1 won't have the N+2 APIs? `__builtin_available(android N+2)` when run on a preview of N+1 would pass and the call would segfault, right? That would be a regression. There's currently no correct use of `__builtin_available` that will cause an unavailable API to be called.

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