Add the list of failing submodules to QtSynchronizeRepo summary

It's easier to see what submodules fail to synchronize and make
the actions on them, rather than looking into full log.

Change-Id: I98bb3b42783e431a53e536e8104a460ba6bc63e9
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

cmake/QtTopLevelHelpers.cmake

@@ -1401,6 +1401,7 @@ function(qt_internal_foreach_repo_run)
         set(color "--red")
     endif()
 
+    set(failing_modules "")
     foreach(module IN LISTS modules)
         message("Entering '${module}'")
         execute_process(
@@ -1418,6 +1419,7 @@ function(qt_internal_foreach_repo_run)
                 ${CMAKE_COMMAND} -E cmake_echo_color "${color}"
                 "Process execution failed here ^^^^^^^^^^^^^^^^^^^^"
             )
+            list(APPEND failing_modules "${module}")
         else()
             math(EXPR count_success "${count_success}+1")
         endif()
@@ -1439,6 +1441,15 @@ function(qt_internal_foreach_repo_run)
             ${CMAKE_COMMAND} -E env CLICOLOR_FORCE=1
             ${CMAKE_COMMAND} -E cmake_echo_color "${color}" "${count_failure}"
     )
+    if(failing_modules)
+        list(JOIN failing_modules ", " failing_modules)
+        execute_process(
+            COMMAND
+                ${CMAKE_COMMAND} -E cmake_echo_color --normal
+                    "Failing submodules: ${failing_modules}"
+        )
+    endif()
+
     message("Successes: ${count_success}")
 endfunction()