libgcc, Darwin: Don't build legacy libgcc_s.1 on macOS 14 [PR116809]

d9cafa0c stopped building libgcc_s.1 on macOS >= 15, in part because
that is required to bootstrap the compiler using the macOS 15 SDK. The
macOS 15 SDK ships in Xcode 16, which also runs on macOS 14. libgcc_s.1
can no longer be built on macOS 14 using Xcode 16 by the same logic that
the previous change disabled it for macOS 15.

	PR target/116809

libgcc/ChangeLog:

	* config.host: Don't build legacy libgcc_s.1 on macOS 14.

Signed-off-by: Mark Mentovai <mark@mentovai.com>