Fix copyright and use consistent C89 comments

src/core/support/stack_lockfree.c

 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -99,8 +99,8 @@ gpr_stack_lockfree *gpr_stack_lockfree_create(size_t entries) {
 
   /* Point the head at reserved dummy entry */
   stack->head.contents.index = INVALID_ENTRY_INDEX;
+  /* Fill in the pad and aba_ctr to avoid confusing memcheck tools */
 #ifdef GPR_ARCH_64
-  // Fill in the pad to avoid confusing memcheck tools
   stack->head.contents.pad = 0;
 #endif
   stack->head.contents.aba_ctr = 0;
@@ -121,7 +121,7 @@ int gpr_stack_lockfree_push(gpr_stack_lockfree *stack, int entry) {
   /* First fill in the entry's index and aba ctr for new head */
   newhead.contents.index = (uint16_t)entry;
 #ifdef GPR_ARCH_64
-  // Fill in the pad to avoid confusing memcheck tools
+  /* Fill in the pad to avoid confusing memcheck tools */
   newhead.contents.pad = 0;
 #endif