Add CMake guards for `dune-subgrid` dependency

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Not released yet
 
+- 2022-05-25: Add CMake guards to prevent build targe generation of cases that depend of `dune-subgrid`, if `dune-subgrid` is not installed.
 - 2022-05-24: Added missing include of `limits` in `couplingadapter.cc`.
 - 2022-05-17: Added base setup for extended documentation to be hosted on ReadTheDocs and being created by `mkdocs`. Also adds a base configuration and style of the documentation.
 - 2022-05-17: Added configuation for Markdown linter `markdownlint` and added it to CI. The linter can be called locally by typing `mdl .` from the root of the repository. This also led to an updated configuration of the CI.

examples/ff-pm/monolithic/CMakeLists.txt

@@ -4,4 +4,6 @@
 add_subdirectory(td-ff-pm-2d-chaabani) # Chaabani et al.
 
 # 3D cases
-add_subdirectory(flow-over-step-3d) # Chaabani et al.
+if ( dune-subgrid_FOUND )
+    add_subdirectory(flow-over-step-3d) # Chaabani et al.
+endif()
\ No newline at end of file

test/monolithic/CMakeLists.txt

 # 2D cases
 add_subdirectory(flow-over-square-2d)
-add_subdirectory(flow-over-step-2d) # Chaabani et al.
+if ( dune-subgrid_FOUND )
+    add_subdirectory(flow-over-step-2d) # Chaabani et al.
+endif()
 # 3D cases
 add_subdirectory(ff-pm-3d)
\ No newline at end of file