Fix side CMake issues.

+ Make HIP on CUDA platform not do the CMAKE_CUDA_COMPILER_VERSION
  check.
+ Fix an important bug affecting the CMAKE_REQUIRED_LIBRARIES management
  of build_type_helpers.cmake.

Co-authored-by: Yuhsiang Tsai <yhmtsai@gmail.com>
Co-authored-by: Tobias Ribizel <ribizel@kit.edu>

cmake/build_type_helpers.cmake

@@ -88,10 +88,9 @@ foreach(_LANG IN LISTS ENABLED_LANGUAGES ITEMS "HIP")
                 ${PROJECT_NAME}_${_LANG}_${_TYPE}_SUPPORTED)
         else()
             if(DEFINED ${PROJECT_NAME}_${_LANG}_${_TYPE}_SUPPORTED)
-                message(STATUS "Skipping ${_LANG}, not supported by build_type.cmake script")
+                message(STATUS "Skipping ${_LANG}, not supported by build_type_helpers.cmake script")
             endif()
             set(${PROJECT_NAME}_${_LANG}_${_TYPE}_SUPPORTED FALSE)
-            continue()
         endif()
         if(${PROJECT_NAME}_${_LANG}_${_TYPE}_SUPPORTED)
             if(_LANG STREQUAL "HIP" AND GINKGO_HIP_PLATFORM MATCHES "${HIP_PLATFORM_NVIDIA_REGEX}")

hip/CMakeLists.txt

@@ -1,5 +1,5 @@
 if (GINKGO_HIP_PLATFORM MATCHES "${HIP_PLATFORM_NVIDIA_REGEX}"
-    AND CMAKE_CUDA_COMPILER_VERSION VERSION_LESS 9.2)
+    AND GINKGO_BUILD_CUDA AND CMAKE_CUDA_COMPILER_VERSION VERSION_LESS 9.2)
     message(FATAL_ERROR "Ginkgo HIP backend requires CUDA >= 9.2.")
 endif()