cmake: Print error output when failing to fetch emcc version information. (#18183)

Author: nmoinvaz

cmake/Modules/Platform/Emscripten.cmake

@@ -100,7 +100,9 @@ set(CMAKE_CXX_COMPILER_RANLIB "${CMAKE_RANLIB}" CACHE FILEPATH "Emscripten ranli
 if (NOT EMSCRIPTEN_VERSION)
   execute_process(COMMAND "${CMAKE_C_COMPILER}" "-v" RESULT_VARIABLE _cmake_compiler_result ERROR_VARIABLE _cmake_compiler_output OUTPUT_QUIET)
   if (NOT _cmake_compiler_result EQUAL 0)
-    message(FATAL_ERROR "Failed to fetch Emscripten version information with command \"'${CMAKE_C_COMPILER}' -v\"! Process returned with error code ${_cmake_compiler_result}.")
+    message(FATAL_ERROR "Failed to fetch Emscripten version information with command \"'${CMAKE_C_COMPILER}' -v\"!\n"
+                        "Process returned with error code ${_cmake_compiler_result}.\n"
+                        "Output:\n${_cmake_compiler_output}")
   endif()
   string(REGEX MATCH "emcc \\(.*\\) ([0-9\\.]+)" _dummy_unused "${_cmake_compiler_output}")
   if (NOT CMAKE_MATCH_1)