rs_bindings_from_cc: Expand make variables in user copts.

PiperOrigin-RevId: 574469615
Change-Id: I24544283212d136a2de7dc208f5af85d01c87629

rs_bindings_from_cc/bazel_support/compile_cc.bzl

diff --git a/rs_bindings_from_cc/bazel_support/compile_cc.bzl b/rs_bindings_from_cc/bazel_support/compile_cc.bzl
index 5de5538..468d793 100644
--- a/rs_bindings_from_cc/bazel_support/compile_cc.bzl
+++ b/rs_bindings_from_cc/bazel_support/compile_cc.bzl
@@ -32,6 +32,11 @@
     """
     cc_info = cc_common.merge_cc_infos(cc_infos = cc_infos)
 
+    user_copts = []
+    for copt in getattr(attr, "copts", []):
+        # ctx.expand_make_variables is deprecated, but its replacement ctx.var does not suffice.
+        user_copts.append(ctx.expand_make_variables("copts", copt, {}))
+
     (compilation_context, compilation_outputs) = cc_common.compile(
         name = src.basename,
         actions = ctx.actions,
@@ -39,7 +44,7 @@
         cc_toolchain = cc_toolchain,
         srcs = [src],
         additional_inputs = extra_cc_compilation_action_inputs,
-        user_compile_flags = attr.copts if hasattr(attr, "copts") else [],
+        user_compile_flags = user_copts,
         compilation_contexts = [cc_info.compilation_context],
     )