Set ENOSYS for all libc dummies

This is a brute-force approach to issue #102. This might be a bit too
much. I don't know if we can clobber errno for all of those?

libports/src/lib/libc/dummies.cc

@@ -13,13 +13,18 @@
 
 #include <base/printf.h>
 #include <stddef.h>
+#include <errno.h>
 
 extern "C" {
 
 	typedef long DUMMY;
 
 #define DUMMY(retval, name) __attribute__((weak))		\
-	DUMMY name(void) { PDBG( #name " called, not implemented"); return retval; }
+DUMMY name(void) {						\
+	PDBG( #name " called, not implemented");		\
+	errno = ENOSYS;						\
+	return retval;						\
+}
 
 DUMMY(-1, access)
 DUMMY(-1, chmod)