The current setup uses the legacy crosstool approach. This makes it harder to add/change toolchains and potentially creates unnecessary cache misses because of differing platform selections. It also complicates migration to Bazel 7.x which flips `–incompatible_cc_toolchain_resolution` and makes it harder to use Bzlmod as most bazel modules rely on the new toolchain resolution mechanism.

Flip `--incompatible_cc_toolchain_resolution` and remove compiler specificity from platform information to cleanly separate buildtime requirements (via toolchain configs) from runtime requirements (via platforms).