pw_toolchain: Transition flag to update rules_cc

Adds temporary migration flag so rules_cc can be updated across
downstream projects.

Bug: b/384050813
Change-Id: I9df89a45d858e29d9537cd02bdfac654f284dbf1
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/254432
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed-service-accounts.iam.gserviceaccount.com>
Docs-Not-Needed: Armando Montanez <amontanez@google.com>
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ted Pudlik <tpudlik@google.com>
Pigweed-Auto-Submit: Armando Montanez <amontanez@google.com>

pw_toolchain/host_clang/BUILD.bazel

@@ -248,8 +248,37 @@ cc_args(
 )
 
 cc_feature(
-    name = "supports_pic",
+    name = "supports_pic_old",
     overrides = "@rules_cc//cc/toolchains/features:supports_pic",
+    visibility = ["//visibility:private"],
+)
+
+# TODO: https://pwbug.dev/384050813 - This flag is a temporary transition flag
+# that will be removed shortly.
+bool_flag(
+    name = "new_rules_cc",
+    build_setting_default = False,
+)
+
+config_setting(
+    name = "rules_cc_post_0.0.10",
+    flag_values = {
+        ":new_rules_cc": "True",
+    },
+)
+
+cc_feature(
+    name = "supports_pic_actual",
+    feature_name = "supports_pic",
+    visibility = ["//visibility:private"],
+)
+
+alias(
+    name = "supports_pic",
+    actual = select({
+        ":rules_cc_post_0.0.10": "supports_pic_actual",
+        "//conditions:default": "supports_pic_old",
+    }),
 )
 
 # Symlink to clangd, for user convenience.