Change the way explain codes are handled to generate the command for the
user to get the explanations, as this was not working for warnings.
gcc/ada/
* errout.adb (Error_Msg_Internal): Remove call to
Prescan_Message on the special continuation for the explain code
command, as this does not play well with the setting of global
variables for the message (like its status as a warning or not).
Instead, set directly the global variables regarding content of
the message in terms of special characters.