Explicitly set `--apple_platform_type` to `macos` when building for MacOS.
This copied from TF's .bazelrc.
@@ -47,6 +47,9 @@ build:linux --copt=-Wno-maybe-uninitialized
# more information.
build:macos --copt=-DGRPC_BAZEL_BUILD
+# Sets the default Apple platform to macOS.
+build:macos --apple_platform_type=macos
+
#
# Remote execution capabilities.
#
