Fix target conflict when generating the same msg files in several subprojects

pom.xml

@@ -9,7 +9,7 @@
 
     <groupId>de.monticore.lang.monticar</groupId>
     <artifactId>embedded-montiarc-math-middleware-generator</artifactId>
-    <version>0.0.15-SNAPSHOT</version>
+    <version>0.0.16-SNAPSHOT</version>
 
 
     <!-- == PROJECT DEPENDENCIES ============================================= -->

src/main/java/de/monticore/lang/monticar/generator/middleware/DistributedTargetGenerator.java

@@ -70,18 +70,12 @@ public class DistributedTargetGenerator extends CMakeGenerator {
     protected File generateCMake(EMAComponentInstanceSymbol componentInstanceSymbol) throws IOException {
         FileContent fileContent = new FileContent();
         fileContent.setFileName("CMakeLists.txt");
-        StringBuilder content = new StringBuilder();
-        content.append("cmake_minimum_required(VERSION 3.5)\n");
-        //TODO setProjectName?
-        content.append("project (default)\n");
-        content.append("set (CMAKE_CXX_STANDARD 11)\n");
 
-        subDirs.stream().filter(dir -> dir.equals("rosMsg")).forEach(
-                dir -> content.append("add_subdirectory(" + dir + ")\n")
-        );
+        StringBuilder content = new StringBuilder();
+        content.append(TemplateHelper.getSubprojectsCMake());
 
-        subDirs.stream().filter(dir -> !dir.equals("rosMsg")).forEach(
-                dir -> content.append("add_subdirectory(" + dir + ")\n")
+        subDirs.forEach(
+                dir -> content.append("add_subdir_without_target_import(" + dir + ")\n")
         );
 
         fileContent.setFileContent(content.toString());

src/main/java/de/monticore/lang/monticar/generator/middleware/helpers/TemplateHelper.java

@@ -48,4 +48,8 @@ public class TemplateHelper {
         return getTemplate("coordinatorCmakeListsTemplate.ftl");
     }
 
+    public static String getSubprojectsCMake() {
+        return getTemplate("SubprojectsCMakeListsTemplate.ftl");
+
+    }
 }

src/main/resources/de/monticore/lang/monticar/generator/middleware/SubprojectsCMakeListsTemplate.ftl

+cmake_minimum_required(VERSION 3.5)
+project (default)
+set (CMAKE_CXX_STANDARD 14)
+
+include(${CMAKE_ROOT}/Modules/ExternalProject.cmake)
+function(add_subdir_without_target_import subdir)
+    ExternalProject_Add(
+        _${subdir}
+        DOWNLOAD_COMMAND ""
+        INSTALL_COMMAND cmake -E echo "Skipping install step."
+        SOURCE_DIR ${CMAKE_SOURCE_DIR}/${subdir}
+        BUILD_ALWAYS 1
+    )
+endfunction(add_subdir_without_target_import)
+