fix cmake script overwriting compiler path

This fixes #2343

cmake/download_test_data.cmake

diff --git a/cmake/download_test_data.cmake b/cmake/download_test_data.cmake
index a3f3f19..f516a7c 100644
--- a/cmake/download_test_data.cmake
+++ b/cmake/download_test_data.cmake
@@ -48,7 +48,7 @@
 # determine the compiler (for debug and support purposes)
 if (MSVC)
     execute_process(COMMAND ${CMAKE_CXX_COMPILER} OUTPUT_VARIABLE CXX_VERSION_RESULT OUTPUT_STRIP_TRAILING_WHITESPACE ERROR_VARIABLE CXX_VERSION_RESULT ERROR_STRIP_TRAILING_WHITESPACE)
-    set(CMAKE_CXX_COMPILER "${CXX_VERSION_RESULT}; MSVC_VERSION=${MSVC_VERSION}; MSVC_TOOLSET_VERSION=${MSVC_TOOLSET_VERSION}")
+    set(CXX_VERSION_RESULT "${CXX_VERSION_RESULT}; MSVC_VERSION=${MSVC_VERSION}; MSVC_TOOLSET_VERSION=${MSVC_TOOLSET_VERSION}")
 else()
     execute_process(COMMAND ${CMAKE_CXX_COMPILER} --version OUTPUT_VARIABLE CXX_VERSION_RESULT OUTPUT_STRIP_TRAILING_WHITESPACE)
 endif()