fixes compile error of network_tcp.c when open is added as cmake subd…

…irectory

arch/CMakeLists.txt

@@ -1,7 +1,7 @@
 SET(SOURCE_GROUP ${SOURCE_GROUP}\\arch)
 
 ua_include_directories(${CMAKE_CURRENT_SOURCE_DIR}) # to have access to ua_network_tcp.h
-ua_include_directories(${CMAKE_SOURCE_DIR}/src) # to have access to ua_securechannel.h
+ua_include_directories(${PROJECT_SOURCE_DIR}/src) # to have access to ua_securechannel.h
 
 add_subdirectory(posix)
 add_subdirectory(win32)