-dnl -W* as gcc cannot test for negated warnings.
-dnl CC_CHECK_FLAG_APPEND([WHERE-TO-APPEND], [ENV-VAR], [FLAG])
+dnl -W* as gcc cannot test for negated warnings. If a C snippet is passed,
+dnl use it, otherwise use a simple main() definition that just returns 0.
+dnl CC_CHECK_FLAG_APPEND([WHERE-TO-APPEND], [ENV-VAR], [FLAG], [C-SNIPPET])