*** Reason for rollback ***

Breaks builds internally.

*** Original change description ***

Move Apple toolchain setup to apple_support

This moves the CC toolchain for building Apple platforms besides macOS to the apple_support repo https://github.com/bazelbuild/apple_support/pull/113

The default unix toolchain is now used if someone wants to build for macOS without the apple_support toolchain, but it doesn't handle as many platform specific features as the previous toolchain.

Fixes https://github.com/bazelbuild/bazel/issues/1...

***

PiperOrigin-RevId: 516486823
Change-Id: If9b2542699cf8704e0a511e684d8519468ddd937