Add stdbool.h to ape

in accordance with c99:7.16. Used by perl, trivial enough
that I feel ok with adding it before the port is fully done.

sys/include/ape/stdbool.h

@@ -0,0 +1,12 @@
+#ifndef __STDBOOL_H__
+#define __STDBOOL_H__
+
+/* Strictly speaking, this should be a built-in type. */
+typedef char _Bool;
+
+#define bool _Bool
+#define true 1
+#define false 0
+#define __bool_true_false_are_defined 1
+
+#endif