Merge fix for no-circular-deps header compilation for CUDA

This PR makes sure that all CUDA headers are being compiled with nvcc in the no-circular-deps mode.

Related PR: #783

cmake/build_helpers.cmake

@@ -55,6 +55,14 @@ function(ginkgo_check_headers target)
     list(FILTER HIP_HEADERS EXCLUDE REGEX "^test.*")
 
     set(SOURCES "")
+    # if we have any CUDA files in there, compile everything as CUDA
+    if (CUDA_HEADERS)
+        set(CUDA_HEADERS ${CUDA_HEADERS} ${CXX_HEADERS})
+        set(CXX_HEADERS "")
+        if (HIP_HEADERS) 
+            message(FATAL_ERROR "Mixing CUDA and HIP files in header check")
+        endif()
+    endif()
     foreach(HEADER ${CUDA_HEADERS})
         set(HEADER_SOURCEFILE "${CMAKE_CURRENT_BINARY_DIR}/${HEADER}.cu")
         file(WRITE "${HEADER_SOURCEFILE}" "#include \"${HEADER}\"")