Do not use CROSSTOOL to select cc_toolchain

This is a preparation for flipping
--incompatible_disable_cc_toolchain_label_from_crosstool_proto, which will stop
reading default_toolchain fields from the crosstool and will rely on
cc_toolchain_suite.toolchains containing entries for cpu without compiler.

Migrations docs can be found here:
https://docs.bazel.build/versions/master/skylark/backward-compatibility.html#disallow-using-crosstool-to-select-the-cc_toolchain-label.

RELNOTES: None.
PiperOrigin-RevId: 216470358