[libc][bazel] Support generating public libc headers in Bazel builds.

This requires adding a new dependency on PyYAML so that Bazel is able
to run the `hdrgen` tool hermetically.

See #134780.

Author: jtstogel

utils/bazel/WORKSPACE

@@ -182,6 +182,15 @@ maybe(
     url = "https://github.com/wjakob/nanobind/archive/refs/tags/v2.4.0.tar.gz",
 )
 
+maybe(
+    http_archive,
+    name = "pyyaml",
+    build_file = "@llvm-raw//utils/bazel/third_party_build:pyyaml.BUILD",
+    sha256 = "f0a35d7f282a6d6b1a4f3f3965ef5c124e30ed27a0088efb97c0977268fd671f",
+    strip_prefix = "pyyaml-5.1/lib3",
+    url = "https://github.com/yaml/pyyaml/archive/refs/tags/5.1.zip",
+)
+
 load("@rules_python//python:repositories.bzl", "py_repositories", "python_register_toolchains")
 
 py_repositories()