Make test/development related makefile vars lazy

They were trying to run `hostname` and `which`, which produced a bunch
of error messages in a hermetic build environment.

And performance of those `shell` calls is not very important, as they
are caled just a few times during script runtime anyway (there is a
hack to make these lazy, but evaluating only once - but it's hardly
worth it).

deps/rabbit_common/mk/rabbitmq-run.mk

@@ -67,12 +67,12 @@ node_enabled_plugins_file = $(call node_tmpdir,$(1))/enabled_plugins
 
 # Broker startup variables for the test environment.
 ifeq ($(PLATFORM),msys2)
-HOSTNAME := $(COMPUTERNAME)
+HOSTNAME = $(COMPUTERNAME)
 else
 ifeq ($(PLATFORM),solaris)
-HOSTNAME := $(shell hostname | sed 's@\..*@@')
+HOSTNAME = $(shell hostname | sed 's@\..*@@')
 else
-HOSTNAME := $(shell hostname -s)
+HOSTNAME = $(shell hostname -s)
 endif
 endif
 
@@ -265,8 +265,8 @@ endif
 endif
 
 run-broker run-tls-broker: RABBITMQ_CONFIG_FILE := $(basename $(TEST_CONFIG_FILE))
-run-broker:     config := $(test_rabbitmq_config)
-run-tls-broker: config := $(test_rabbitmq_config_with_tls)
+run-broker:     config = $(test_rabbitmq_config)
+run-tls-broker: config = $(test_rabbitmq_config_with_tls)
 run-tls-broker: $(TEST_TLS_CERTS_DIR)
 
 run-broker run-tls-broker: node-tmpdir $(DIST_TARGET) $(TEST_CONFIG_FILE)

deps/rabbit_common/mk/rabbitmq-tools.mk

@@ -1,10 +1,10 @@
 ifeq ($(PLATFORM),msys2)
-HOSTNAME := $(COMPUTERNAME)
+HOSTNAME = $(COMPUTERNAME)
 else
 ifeq ($(PLATFORM),solaris)
-HOSTNAME := $(shell hostname | sed 's@\..*@@')
+HOSTNAME = $(shell hostname | sed 's@\..*@@')
 else
-HOSTNAME := $(shell hostname -s)
+HOSTNAME = $(shell hostname -s)
 endif
 endif
 

mk/bazel.mk

@@ -28,7 +28,7 @@ build --flaky_test_attempts=1
 build:buildbuddy --remote_header=x-buildbuddy-api-key=YOUR_API_KEY
 endef
 
-export USER_BAZELRC
+user.bazelrc: export USER_BAZELRC
 user.bazelrc:
 	echo "$$USER_BAZELRC" > $@