-# Checks for libraries.
-AC_CHECK_LIB([m], [powl])
-# FIXME: Replace `main' with a function in `-lpopulation':
+if test "x$GCC" = "xyes"
+then
+ CFLAGS="$CFLAGS -std=c99"
+fi
+
+AC_DEFINE([_ISOC99_SOURCE], [1], [Define to use C99])
+AC_DEFINE([_POSIX_C_SOURCE], [200809L], [Set to desired POSIX version])
+AC_DEFINE([_XOPEN_SOURCE], [700], [Set to desired X/Open version])
+
+# TODO: Write check for libpopulation