Hi!
Go to "Preferences" in "File" menu, then enable
"Allow implicit declaration of functions" checkbox.
Your idle_loop declaration is implicit ('int' or 'void'
is missing), and IDE allow this only if this checkbox
is enabled.
By the way, Sebastian, please make setup to check this
checkbox by default: we will receive a dozens of such
questions!
Cheers,
Zeljko Juric