subprojects: add errno

Version 0.3.12 in:

     - Fedora
       (https://packages.fedoraproject.org/pkgs/rust-errno/rust-errno+default-devel/)
     - AOSP (0.3.8, but should still work)

Acked-by: Aaron Ruby <aruby@qnx.com>
Reviewed-by: @LingMan
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35210>

subprojects/packagefiles/errno/meson.build

@@ -0,0 +1,24 @@
+# Copyright © 2025 Google
+# SPDX-License-Identifier: MIT
+
+project(
+  'errno',
+  'rust',
+  version : '0.3.12',
+  license : 'MIT OR Apache-2.0',
+)
+
+libc = subproject('libc').get_variable('lib')
+
+lib = static_library(
+  'libc_errno',
+  'src/lib.rs',
+  override_options : ['rust_std=2018', 'build.rust_std=2018'],
+  link_with: [libc],
+  rust_abi : 'rust',
+  native : true,
+)
+
+dep_errno = declare_dependency(
+  link_with : [lib]
+)