Switch image version 1.3 and add VF_MPI compiler definition again for gpu version as well.

.devcontainer/devcontainer.json

-{  
+{
     "name": "virtual-fluids-environment",
     "extensions": [
         "mhutchie.git-graph",
@@ -11,5 +11,5 @@
         "streetsidesoftware.code-spell-checker"
     ],
     "runArgs": ["--gpus","all"],
-    "image": "git.rz.tu-bs.de:4567/irmb/virtualfluids/ubuntu20_04:1.2"
+    "image": "git.rz.tu-bs.de:4567/irmb/virtualfluids/ubuntu20_04:1.3"
 }

CMakeLists.txt

@@ -170,9 +170,7 @@ endif()
 
 if(BUILD_USE_MPI)
     find_package(MPI REQUIRED)
-    if(BUILD_VF_CPU)
-        list(APPEND VF_COMPILER_DEFINITION VF_MPI)
-    endif()
+    list(APPEND VF_COMPILER_DEFINITION VF_MPI)
 endif()
 
 # boost