bazelrc: Enable experimental_platform_in_output_dir

With Bazel 5 available we can now enable this experimental flag. This
behavior is desirable to allow switching between platform targets
without clobbering the existing bazel-out/ directory and throwing away
work.

BUG=b:213616502
TEST=local drydock build

Change-Id: Idadaf284ed211fbe1d271512035d4a3fff75cd57
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/rules_cros/+/3437430
diff --git a/common.bazelrc b/common.bazelrc
index 507c816..96a6ca0 100644
--- a/common.bazelrc
+++ b/common.bazelrc
@@ -1,6 +1,11 @@
 # Assume we're building on x86_64 Linux for now.
 build --host_platform @rules_cros//cros/platforms:linux_x86_64
 
+# Use the target platform in the bazel-out/ output directory name fragment
+# instead of the CPU (darwin, k8). This avoids thrashing the output directory
+# when switching between top level target --platforms values.
+build --experimental_platform_in_output_dir
+
 # Use the JDK provided by the CrOS SDK instead of trying to download a bundled
 # remote JDK.
 build --tool_java_runtime_version=11