Avoid using same variable name as it leads to recursive calls.

coupler/opc-ua-server/Makefile

-CC=$(CC)
+CC=$(C_COMPILER)
 CFLAGS= -I $(OPEN62541_SOURCE_HOME) 
 LDFLAGS= -L $(OPEN62541_HOME)/lib
 OUT_DIR= $(BINARY_OUT_DIR)

slapos/software/osie-coupler/software-opc-ua.cfg

@@ -50,7 +50,7 @@ location = ${buildout:parts-directory}/osie
 recipe = slapos.recipe.cmmi
 path = ${osie-repository:location}/coupler/opc-ua-server/
 environment =
-  CC = arm-linux-gnueabihf-gcc
+  C_COMPILER = arm-linux-gnueabihf-gcc
   OPEN62541_HOME = ${open62541:location}
   OPEN62541_SOURCE_HOME = ${open62541-source:location}
   BINARY_OUT_DIR = ${buildout:directory}/bin