Auto merge of #146513 - madsmtm:apple-reenable-assertions, r=Mark-Simulacrum

Re-enable assertions on macOS alt builds

These were previously disabled, in part for performance reasons, in part due to needing availability symbols `__isPlatformVersionAtLeast` and `__isOSVersionAtLeast` that `compiler-builtins` did not provide, see rust-lang/rust#62592 (comment) and rust-lang/rust#134275 (comment) for failed checks.

Since rust-lang/rust#138944 though, `std` now provides these symbols, so we should be able to re-enable LLVM assertions, debug assertions and overflow checks.

Fixes rust-lang/rust#59637.

try-job: `*apple*`

Author: bors