6977924: Changes for 6975078 produce build error with certain gcc versions

Summary: The changes introduced for 6975078 assign badHeapOopVal to the _allocation field in the ResourceObj class. In 32 bit linux builds with certain versions of gcc this assignment will be flagged as an error while compiling allocation.cpp. In 32 bit builds the constant value badHeapOopVal (which is cast to an intptr_t) is negative. The _allocation field is typed as an unsigned intptr_t and gcc catches this as an error.
Reviewed-by: jcoomes, ysr, phh

src/share/vm/memory/allocation.cpp

@@ -58,7 +58,7 @@ void* ResourceObj::operator new(size_t size, allocation_type type) {
 void ResourceObj::operator delete(void* p) {
   assert(((ResourceObj *)p)->allocated_on_C_heap(),
          "delete only allowed for C_HEAP objects");
-  DEBUG_ONLY(((ResourceObj *)p)->_allocation = badHeapOopVal;)
+  DEBUG_ONLY(((ResourceObj *)p)->_allocation = (uintptr_t) badHeapOopVal;)
   FreeHeap(p);
 }
 
@@ -104,7 +104,7 @@ ResourceObj& ResourceObj::operator=(const ResourceObj& r) { // default copy assi
 ResourceObj::~ResourceObj() {
     // allocated_on_C_heap() also checks that encoded (in _allocation) address == this.
     if (!allocated_on_C_heap()) {  // ResourceObj::delete() zaps _allocation for C_heap.
-      _allocation = badHeapOopVal; // zap type
+      _allocation = (uintptr_t) badHeapOopVal; // zap type
     }
 }
 #endif // ASSERT