linux-info.eclass: fix error/warning messages with ~!SYMBOLS

For ebuilds that do things like ~!IDE, the current warning system would
drop the ~ but not the !.  This would lead to doing variable expansion
like ${WARNING_!IDE} which is invalid shell code.

eclass/linux-info.eclass

@@ -716,13 +716,15 @@ check_extra_config() {
  ewarn "to absence of any configured kernel sources or compiled"
  ewarn "config:"
  for config in ${CONFIG_CHECK}; do
- local_error="ERROR_${config#\~}"
+ config=${config#\~}
+ config=${config#\!}
+ local_error="ERROR_${config}"
  msg="${!local_error}"
- if [[ "x${msg}" == "x" ]]; then
- local_error="WARNING_${config#\~}"
+ if [[ -z ${msg} ]]; then
+ local_error="WARNING_${config}"
  msg="${!local_error}"
  fi
- ewarn " - ${config#\~}${msg:+ - }${msg}"
+ ewarn " - ${config}${msg:+ - }${msg}"
  done
  ewarn "You're on your own to make sure they are set if needed."
  export LINUX_CONFIG_EXISTS_DONE="${old_LINUX_CONFIG_EXISTS_DONE}"