Suppress warnings from external repositories if possible

.bazelrc

@@ -1,4 +1,4 @@
-# Copyright 2021, 2022, 2023 Google LLC
+# Copyright 2021, 2022, 2023, 2024 Google LLC
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -12,6 +12,15 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+common --enable_platform_specific_config
+
+# Suppress warnings from external repositories if possible.
+build --features=external_include_paths
+build --host_features=external_include_paths
+
+# FIXME: This shouldn’t be necessary.  File bug against Bazel.
+build:windows --copt='/external:W3' --host_copt='/external:W3'
+
 # Run Pylint by default.
 build --aspects='//private:defs.bzl%check_python'
 build --output_groups='+check_python'

emacs/defs.bzl

@@ -204,4 +204,4 @@ def _install(ctx, cc_toolchain, readme):
 
 def _munge_msvc_flag(s):
     # Crude way to work around specifying Visual C++ options in .bazelrc.
-    return s.replace("/std:c", "-std=gnu")
+    return None if s.startswith("/external:") else s.replace("/std:c", "-std=gnu")