[cmake] Add opcua to configuration.

  - The Makefile based OM build system copies the files in the open62541
    folder to SimulationRuntime/c/opc/ua and then compiles them there.

    There is no need to do that. Either just move the files there
    completely or create a library here and link to it there.

    The CMake build does the latter. There is a tiny library,
    libopcua (a.k.a omc::3rd::opcua), created here that can be linked to
    when needed.

CMakeLists.txt

@@ -135,6 +135,9 @@ add_library(omc::3rd::Modelica::IO ALIAS ModelicaIO)
 add_library(omc::3rd::Modelica::StandardTables ALIAS ModelicaStandardTables)
 
 
+omc_add_subdirectory(open62541)
+add_library(omc::3rd::opcua ALIAS opcua)
+
 # Intel TBB
 # set(TBB_BUILD_TESTS OFF CACHE BOOL "Build TBB tests and enable testing infrastructure")
 # set(TBB_BUILD_SHARED OFF CACHE BOOL "Build TBB shared library")

open62541/CMakeLists.txt

@@ -0,0 +1,7 @@
+cmake_minimum_required(VERSION 3.14)
+project(opcua)
+
+add_library(opcua STATIC)
+target_sources(opcua PRIVATE open62541.c)
+
+target_include_directories(opcua PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})