Name function arguments in libc headers for Studio.

Second batch of headers...

Bug: http://b/64613623
Test: builds
Change-Id: I8eef043dbf32afee8ff814e9d005f46aee8fa21f
diff --git a/libc/include/sys/reg.h b/libc/include/sys/reg.h
index 1066b6d..6c496ba 100644
--- a/libc/include/sys/reg.h
+++ b/libc/include/sys/reg.h
@@ -83,4 +83,4 @@
 
 #endif
 
-#endif /* _SYS_REG_H_ */
+#endif