fixup! Makefile: WORKER_FEATURES should not overwrite user supplied value

Author: OverOrion

Makefile

@@ -77,12 +77,12 @@ ifeq ($(SGX_PRODUCTION), 1)
 	SGX_ENCLAVE_MODE = "Production Mode"
 	SGX_ENCLAVE_CONFIG = "enclave-runtime/Enclave.config.production.xml"
 	SGX_SIGN_KEY = $(SGX_COMMERCIAL_KEY)
-	WORKER_FEATURES += --features=production,$(WORKER_MODE),$(ADDITIONAL_FEATURES)
+	WORKER_FEATURES := --features=production,$(WORKER_MODE),$(WORKER_FEATURES),$(ADDITIONAL_FEATURES)
 else
 	SGX_ENCLAVE_MODE = "Development Mode"
 	SGX_ENCLAVE_CONFIG = "enclave-runtime/Enclave.config.xml"
 	SGX_SIGN_KEY = "enclave-runtime/Enclave_private.pem"
-	WORKER_FEATURES += --features=default,$(WORKER_MODE),$(ADDITIONAL_FEATURES)
+	WORKER_FEATURES := --features=default,$(WORKER_MODE),$(WORKER_FEATURES),$(ADDITIONAL_FEATURES)
 endif
 
 CLIENT_FEATURES = --features=$(WORKER_MODE),$(ADDITIONAL_FEATURES)