Move legacy_fields_migrator to rules_cc

Needed for --incompatible_disable_legacy_crosstool_fields migration: https://github.com/bazelbuild/bazel/issues/6861
Tracking issue: https://github.com/bazelbuild/bazel/issues/5883

RELNOTES: None.
PiperOrigin-RevId: 225956311
4 files changed
tree: 7324de2947e457ac7d3d696847934da4d8589320
  1. third_party/
  2. tools/
  3. BUILD
  4. LICENSE