last-minute fix: convert to ANSI C

R=dmr
DELTA=3  (2 added, 0 deleted, 1 changed)
diff --git a/src/pkg/debug/macho/testdata/hello.c b/src/pkg/debug/macho/testdata/hello.c
index 8626b30..a689d36 100644
--- a/src/pkg/debug/macho/testdata/hello.c
+++ b/src/pkg/debug/macho/testdata/hello.c
@@ -1,6 +1,8 @@
 #include <stdio.h>
 
-main()
+int
+main(void)
 {
 	printf("hello, world\n");
+	return 0;
 }