last-minute fix: convert to ANSI C

R=dmr
DELTA=3  (2 added, 0 deleted, 1 changed)

Author: Brian Kernighan

src/pkg/debug/macho/testdata/hello.c

@@ -1,6 +1,8 @@
 #include <stdio.h>
 
-main()
+int
+main(void)
 {
 	printf("hello, world\n");
+	return 0;
 }