kokkos: don't repeat CMAKE_CXX_FLAGS when in-tree

kokkos/CMakeLists.txt

@@ -14,6 +14,7 @@ if (KOKKOS_IN_TREE)
     message(STATUS "Building using in-tree kokkos source at `${KOKKOS_IN_TREE}`")
     if(FORWARD_CXX_EXTRA_FLAGS_TO_KOKKOS)
         message(STATUS "Forwarding CXX_EXTRA_FLAGS to Kokkos...")
+        set(OLD_CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}") # save it for now
         set(CMAKE_CXX_FLAGS ${CXX_EXTRA_FLAGS})
     else()
         message(STATUS "Not forwarding CXX_EXTRA_FLAGS to Kokkos by default, set FORWARD_CXX_EXTRA_FLAGS_TO_KOKKOS=ON to override")
@@ -68,6 +69,10 @@ target_compile_options(bude PUBLIC "$<$<CONFIG:RelWithDebInfo>:${RELEASE_OPTIONS
 target_compile_options(bude PUBLIC "$<$<CONFIG:Release>:${RELEASE_OPTIONS}>")
 target_compile_options(bude PUBLIC "$<$<CONFIG:Debug>:${DEBUG_OPTIONS}>")
 
+if(DEFINED OLD_CMAKE_CXX_FLAGS) # restore if overwritten before, as required by Kokkos to pick up CXX_EXTRA_FLAGS as CMAKE_CXX_FLAGS
+    set(CMAKE_CXX_FLAGS ${OLD_CMAKE_CXX_FLAGS})
+endif()
+
 target_link_libraries(bude Kokkos::kokkos)
 
 if (${CMAKE_VERSION} VERSION_LESS "3.13.0")