code review 204065: runtime: allow arbitrary return type in SetFinalizer.

src/pkg/runtime/malloc.h

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // Memory allocator, based on tcmalloc.
 // http://goog-perftools.sourceforge.net/doc/tcmalloc.html
 
 // The main allocator works in runs of pages.
 // Small allocation sizes (up to and including 32 kB) are
 // rounded to one of about 100 size classes, each of which
@@ skipping 300 matching lines @@
 MSpan*  MHeap_LookupMaybe(MHeap *h, PageID p);
 
 void*   mallocgc(uintptr size, uint32 flag, int32 dogc);
 int32   mlookup(void *v, byte **base, uintptr *size, uint32 **ref);
 void    gc(int32 force);
 
 void*   SysAlloc(uintptr);
 void    SysUnused(void*, uintptr);
 void    SysFree(void*, uintptr);
 
-void    addfinalizer(void*, void*);
-void*   getfinalizer(void*, bool);
+void*   getfinalizer(void*, bool, int32*);
 
 enum
 {
         RefcountOverhead = 4,   // one uint32 per object
 
         RefFree = 0,    // must be zero
         RefStack,               // stack segment - don't free and don't scan for pointers
         RefNone,                // no references
         RefSome,                // some references
         RefFinalize,    // ready to be finalized
         RefNoPointers = 0x80000000U,    // flag - no pointers here·····
 };