Returns true if callbacks has yet to be generated and register it as being generated

Property definitions

nitc :: compiler_ffi $ MModule :: check_callback_compilation
	# Returns true if callbacks has yet to be generated and register it as being generated
	private fun check_callback_compilation(cb: NitniCallback): Bool
	do
		var compiled = compiled_callbacks.has(cb)
		if not compiled then compiled_callbacks.add(cb)
		return not compiled
	end
src/compiler/compiler_ffi/compiler_ffi.nit:38,2--44,4