The reverted change silently bumped the minimal macOS SDK required for
building the TSan runtime to SDK 10.12. Let's ensure release 10 does
not unexpectedly break builders with old SDKs and add proper minimal SDK
checking in CMake for subsequent releases.
This reverts commit 894abb46f891cba2e0ef581650f27f512a7824b4.
Fixes bug #44682.