Bazel: Address Copilot review comment

Author: jketema

unified/swift-syntax-rs/BUILD.bazel

@@ -14,6 +14,7 @@ swift_runtime_libs(
 
 swift_runtime_linking(
     name = "_swift_runtime_cc_info",
+    visibility = ["//visibility:private"],
 )
 
 # On Linux, provide the downloaded Swift runtime at link time and look beside
@@ -25,10 +26,7 @@ cc_library(
         "//conditions:default": [],
     }),
     target_compatible_with = UNIFIED_SUPPORTED_PLATFORMS,
-    deps = select({
-        "@platforms//os:linux": [":_swift_runtime_cc_info"],
-        "//conditions:default": [],
-    }),
+    deps = [":_swift_runtime_cc_info"],
 )
 
 # Swift FFI shim: wraps swift-syntax and exposes a small C ABI.

unified/swift-syntax-rs/swift_runtime_linking.bzl

@@ -3,7 +3,8 @@
 load("@rules_swift//swift:swift.bzl", "swift_common")
 
 def _swift_runtime_linking_impl(ctx):
-    return [swift_common.get_toolchain(ctx).dynamic_runtime_cc_info]
+    runtime_cc_info = swift_common.get_toolchain(ctx).dynamic_runtime_cc_info
+    return [runtime_cc_info] if runtime_cc_info else []
 
 swift_runtime_linking = rule(
     implementation = _swift_runtime_linking_impl,