Clarify migration docs for --incompatible_disable_legacy_cpp_toolchain_skylark_api
Clarify migration docs for --incompatible_disable_legacy_cpp_toolchain_skylark_api

RELNOTES: None.
PiperOrigin-RevId: 223131559

twitter-forks/bazel,ulfjack/bazel,werkt/bazel,meteorcloudy/bazel,aehlig/bazel,safarmer/bazel,safarmer/bazel,meteorcloudy/bazel,ulfjack/bazel,cushon/bazel,katre/bazel,cushon/bazel,twitter-forks/bazel,aehlig/bazel,davidzchen/bazel,katre/bazel,davidzchen/bazel,aehlig/bazel,akira-baruah/bazel,katre/bazel,twitter-forks/bazel,ulfjack/bazel,ulfjack/bazel,bazelbuild/bazel,werkt/bazel,perezd/bazel,meteorcloudy/bazel,twitter-forks/bazel,dslomov/bazel-windows,aehlig/bazel,ButterflyNetwork/bazel,davidzchen/bazel,twitter-forks/bazel,perezd/bazel,dslomov/bazel,dslomov/bazel,ButterflyNetwork/bazel,perezd/bazel,cushon/bazel,akira-baruah/bazel,davidzchen/bazel,safarmer/bazel,meteorcloudy/bazel,dslomov/bazel-windows,akira-baruah/bazel,dslomov/bazel,ButterflyNetwork/bazel,werkt/bazel,akira-baruah/bazel,safarmer/bazel,ButterflyNetwork/bazel,ButterflyNetwork/bazel,perezd/bazel,ulfjack/bazel,cushon/bazel,cushon/bazel,dslomov/bazel,twitter-forks/bazel,davidzchen/bazel,werkt/bazel,katre/bazel,safarmer/bazel,bazelbuild/bazel,aehlig/bazel,davidzchen/bazel,cushon/bazel,dslomov/bazel-windows,dslomov/bazel-windows,bazelbuild/bazel,dslomov/bazel-windows,davidzchen/bazel,katre/bazel,perezd/bazel,akira-baruah/bazel,perezd/bazel,bazelbuild/bazel,meteorcloudy/bazel,ulfjack/bazel,ButterflyNetwork/bazel,bazelbuild/bazel,ulfjack/bazel,safarmer/bazel,akira-baruah/bazel,katre/bazel,dslomov/bazel,meteorcloudy/bazel,dslomov/bazel,meteorcloudy/bazel,aehlig/bazel,twitter-forks/bazel,dslomov/bazel,werkt/bazel,aehlig/bazel,werkt/bazel,perezd/bazel,bazelbuild/bazel,dslomov/bazel-windows