*: migrate to CC toolchains and Bazel 5.4.0

Change-Id: Iff3c0ddda4413dd0c5fa657a5b7813223e98611e
Reviewed-on: https://review.monogon.dev/c/monogon/+/1079
Tested-by: Jenkins CI
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
diff --git a/build/platforms/os/BUILD.bazel b/build/platforms/os/BUILD.bazel
new file mode 100644
index 0000000..3775b39
--- /dev/null
+++ b/build/platforms/os/BUILD.bazel
@@ -0,0 +1,9 @@
+package(
+    default_visibility = ["//visibility:public"],
+)
+
+# EFI preboot environment
+constraint_value(
+    name = "efi",
+    constraint_setting = "@platforms//os:os",
+)