CMakeIOSInstallCombined: do not merge content of OUTPUT and ERROR variables

Modules/CMakeIOSInstallCombined.cmake

@@ -237,17 +237,20 @@ function(ios_install_combined target destination)
   endif()
 
   set(cmd xcrun -f lipo)
+
+  # Do not merge OUTPUT_VARIABLE and ERROR_VARIABLE since latter may contain
+  # some diagnostic information even for the successful run.
   execute_process(
       COMMAND ${cmd}
       RESULT_VARIABLE result
       OUTPUT_VARIABLE output
-      ERROR_VARIABLE output
+      ERROR_VARIABLE error_output
       OUTPUT_STRIP_TRAILING_WHITESPACE
       ERROR_STRIP_TRAILING_WHITESPACE
   )
   if(NOT result EQUAL 0)
     message(
-        FATAL_ERROR "Command failed (${result}): ${cmd}\n\nOutput:\n${output}"
+        FATAL_ERROR "Command failed (${result}): ${cmd}\n\nOutput:\n${output}\nOutput(error):\n${error_output}"
     )
   endif()
   set(_lipo_path ${output})