Add open62541's include folder.

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

@@ -58,7 +58,7 @@ environment =
   OPEN62541_HOME = ${open62541:location}
   OPEN62541_SOURCE_HOME = ${open62541-source:location}
   BINARY_OUT_DIR = ${buildout:directory}/bin
-  C_COMPILER_EXTRA_FLAGS = -L ${mbedtls:location}/lib  -lmbedtls -lmbedx509 -lmbedcrypto -l:libopen62541.so -L${open62541:location}/lib
+  C_COMPILER_EXTRA_FLAGS = -L ${mbedtls:location}/lib  -lmbedtls -lmbedx509 -lmbedcrypto -l:libopen62541.so -L${open62541:location}/lib -I${open62541:location}/include
 # actually configure-command is useless here but needed by convention
 configure-command = 
   ${cmake:location}/bin/cmake