Locked down visibility of the new flags and config settings.

PiperOrigin-RevId: 846416610

Author: haberman

bazel/toolchains/BUILD

@@ -3,14 +3,14 @@ load("@bazel_skylib//rules:common_settings.bzl", "bool_flag")
 
 package(
     default_applicable_licenses = ["//:license"],
-    default_visibility = ["//visibility:public"],
 )
 
 bzl_library(
     name = "proto_toolchain_bzl",
     srcs = [
         "proto_toolchain.bzl",
     ],
+    visibility = ["//visibility:public"],
     deps = [
         "//bazel/private:proto_toolchain_rule_bzl",
         "//bazel/private:toolchain_helpers_bzl",
@@ -22,6 +22,7 @@ bzl_library(
     srcs = [
         "proto_lang_toolchain.bzl",
     ],
+    visibility = ["//visibility:public"],
     deps = [
         "//bazel/common:proto_common_bzl",
         "//bazel/private:proto_lang_toolchain_rule_bzl",
@@ -52,6 +53,7 @@ bool_flag(
 config_setting(
     name = "prefer_prebuilt_protoc.flag_set",
     flag_values = {":prefer_prebuilt_protoc": "true"},
+    visibility = ["//bazel/private/toolchains/prebuilt:__pkg__"],
 )
 
 # The public API users set to disable the validation action failing.
@@ -63,4 +65,5 @@ bool_flag(
 config_setting(
     name = "allow_nonstandard_protoc.flag_set",
     flag_values = {":allow_nonstandard_protoc": "true"},
+    visibility = ["//bazel/private/toolchains/prebuilt:__pkg__"],
 )