Add a --test_build flag for building the broker for mixed versions

.bazelrc

@@ -7,6 +7,7 @@ build --local_test_jobs=1
 build --flag_alias=erlang_home=@rules_erlang//:erlang_home
 build --flag_alias=erlang_version=@rules_erlang//:erlang_version
 build --flag_alias=elixir_home=//:elixir_home
+build --flag_alias=test_build=//:enable_test_build
 
 build:buildbuddy --bes_results_url=https://app.buildbuddy.io/invocation/
 build:buildbuddy --bes_backend=grpcs://remote.buildbuddy.io

BUILD.bazel

@@ -1,5 +1,6 @@
 load(
     "@bazel_skylib//rules:common_settings.bzl",
+    "bool_flag",
     "string_flag",
 )
 load("@rules_pkg//:pkg.bzl", "pkg_tar")
@@ -26,6 +27,19 @@ config_setting(
     },
 )
 
+bool_flag(
+    name = "enable_test_build",
+    build_setting_default = False,
+    visibility = ["//visibility:public"],
+)
+
+config_setting(
+    name = "test_build",
+    flag_values = {
+        "//:enable_test_build": "true",
+    },
+)
+
 string_flag(
     name = "elixir_home",
     build_setting_default = "",

rabbitmq.bzl

@@ -135,6 +135,9 @@ def rabbitmq_app(
         erlc_opts = select({
             "//:debug_build": without("+deterministic", RABBITMQ_ERLC_OPTS),
             "//conditions:default": RABBITMQ_ERLC_OPTS,
+        }) + select({
+            "//:test_build": ["-DTEST=1", "+nowarn_export_all"],
+            "//conditions:default": [],
         }),
         build_deps = build_deps,
         deps = deps,