Merge Check of downstream compilers

This merge adds checks of the downstream compilers. An CMake warning will be issued if the project uses different compilers than the installed Ginkgo.
Currently, only the CXX, CUDA, and CUDA_HOST compilers are inspected. The HIP compiler can be added, when our CMake is updated.

cmake/GinkgoConfig.cmake.in

@@ -63,7 +63,6 @@ set(GINKGO_JACOBI_FULL_OPTIMIZATIONS @GINKGO_JACOBI_FULL_OPTIMIZATIONS@)
 
 set(GINKGO_CUDA_ARCHITECTURES "@GINKGO_CUDA_ARCHITECTURES@")
 set(GINKGO_CUDA_DEFAULT_HOST_COMPILER @GINKGO_CUDA_DEFAULT_HOST_COMPILER@)
-set(GINKGO_CUDA_HOST_COMPILER "@CMAKE_CUDA_HOST_COMPILER@")
 set(GINKGO_CUDA_ARCH_FLAGS "@GINKGO_CUDA_ARCH_FLAGS@")
 
 set(GINKGO_HIP_COMPILER_FLAGS "@GINKGO_HIP_COMPILER_FLAGS@")
@@ -91,6 +90,14 @@ set(GINKGO_HAVE_HWLOC @GINKGO_HAVE_HWLOC@)
 
 set(GINKGO_HAVE_ROCTX @GINKGO_HAVE_ROCTX@)
 
+# Ginkgo compiler information
+set(GINKGO_CXX_COMPILER "@CMAKE_CXX_COMPILER@")
+set(GINKGO_CXX_COMPILER_SHORT "@CMAKE_CXX_COMPILER_ID@:@CMAKE_CXX_COMPILER_VERSION@")
+set(GINKGO_CUDA_COMPILER "@CMAKE_CUDA_COMPILER@")
+set(GINKGO_CUDA_COMPILER_SHORT "@CMAKE_CUDA_COMPILER_ID@:@CMAKE_CUDA_COMPILER_VERSION@")
+set(GINKGO_CUDA_HOST_COMPILER "@CMAKE_CUDA_HOST_COMPILER@")
+set(GINKGO_CUDA_HOST_COMPILER_SHORT "")  # dummy value to stay consistent
+
 # Ginkgo installation configuration
 set(GINKGO_INSTALL_PREFIX "@PACKAGE_CMAKE_INSTALL_PREFIX@")
 set(GINKGO_INSTALL_INCLUDE_DIR "@PACKAGE_CMAKE_INSTALL_FULL_INCLUDEDIR@")
@@ -107,7 +114,6 @@ if(GINKGO_BUILD_HIP)
 endif()
 list(APPEND CMAKE_PREFIX_PATH "${GINKGO_INSTALL_PREFIX}")
 
-
 set(GINKGO_INTERFACE_LINK_LIBRARIES "@GINKGO_INTERFACE_LINK_LIBRARIES@")
 set(GINKGO_INTERFACE_LINK_FLAGS "@GINKGO_INTERFACE_LINK_FLAGS@")
 set(GINKGO_INTERFACE_CXX_FLAGS "@GINKGO_INTERFACE_CXX_FLAGS@")
@@ -207,4 +213,20 @@ if((NOT GINKGO_BUILD_SHARED_LIBS) AND GINKGO_HAVE_TAU)
     find_package(PerfStubs REQUIRED)
 endif()
 
+# Check that the same compilers as for Ginkgo are used
+function(_ginkgo_check_compiler lang)
+    if(NOT ${CMAKE_${lang}_COMPILER} STREQUAL ${GINKGO_${lang}_COMPILER})
+        set(_compiler_short "${CMAKE_${lang}_COMPILER_ID}:${CMAKE_${lang}_COMPILER_VERSION}")
+        if(NOT _compiler_short STREQUAL "${GINKGO_${lang}_COMPILER_SHORT}")
+            message(WARNING "The currently used ${lang} compiler: ${CMAKE_${lang}_COMPILER} does not match the compiler used to "
+                            "build Ginkgo: ${GINKGO_${lang}_COMPILER}. It is encouraged to use the same compiler as Ginkgo to prevent ABI mismatch.")
+        endif()
+    endif()
+endfunction()
+_ginkgo_check_compiler(CXX)
+if(GINKGO_BUILD_CUDA)
+    _ginkgo_check_compiler(CUDA)
+    _ginkgo_check_compiler(CUDA_HOST)
+endif()
+
 include(${CMAKE_CURRENT_LIST_DIR}/GinkgoTargets.cmake)