Add //config:platforms bzl_library

Needed to bring rules_apple `bzl_library` dependencies up-to-date.

Signed-off-by: Brentley Jones <[email protected]>

configs/BUILD

@@ -1,3 +1,4 @@
+load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
 load("@bazel_skylib//lib:selects.bzl", "selects")
 load(":platforms.bzl", "APPLE_PLATFORMS_CONSTRAINTS")
 
@@ -43,6 +44,12 @@ selects.config_setting_group(
     ],
 )
 
+bzl_library(
+    name = "platforms",
+    srcs = ["platforms.bzl"],
+    visibility = ["//visibility:public"],
+)
+
 # Consumed by bazel tests.
 filegroup(
     name = "for_bazel_tests",