Add --incompatible_disable_runtimes_filegroups

This change adds cc_toolchain.static_runtime_lib and
cc_toolchain.dynamic_runtime_lib attributes and an incompatible flag that
disables deprecated cc_toolchain.static_runtime_libs and
cc_toolchain.dynamic_runtime_libs.

Issue for the incompatible flag: #6942
Tracking issue for legacy crosstool fields removal: #5883

RELNOTES: Added --incompatible_disable_runtimes_filegroups
(https://github.com/bazelbuild/bazel/issues/6942).
PiperOrigin-RevId: 226165743
diff --git a/third_party/com/github/bazelbuild/bazel/src/main/protobuf/crosstool_config.proto b/third_party/com/github/bazelbuild/bazel/src/main/protobuf/crosstool_config.proto
index 1d8b58f..2abf053 100644
--- a/third_party/com/github/bazelbuild/bazel/src/main/protobuf/crosstool_config.proto
+++ b/third_party/com/github/bazelbuild/bazel/src/main/protobuf/crosstool_config.proto
@@ -360,7 +360,9 @@
   // If specified, Blaze finds statically linked / dynamically linked runtime
   // libraries in the declared crosstool filegroup. Otherwise, Blaze
   // looks in "[static|dynamic]-runtime-libs-$TARGET_CPU".
+  // Deprecated, see https://github.com/bazelbuild/bazel/issues/6942
   optional string static_runtimes_filegroup = 45;
+  // Deprecated, see https://github.com/bazelbuild/bazel/issues/6942
   optional string dynamic_runtimes_filegroup = 46;
   optional bool supports_incremental_linker = 41 [default = false];
   // This should be true, if the toolchain supports the D flag to ar, which