Fix IsSameObject()

Commit 95ed3a5 ("compiler-rt: Optimize IsSameObject()") introduced
a bug where an object address was wrongly compared with a metadata
address.

The idea behind optimization was based on the assumption that if the
metadata from two different addresses is the same, they must belong to
the same object.

Let's fix it :)

compiler-rt/lib/plsan/plsan_allocator.cpp

@@ -60,7 +60,7 @@ bool IsSameObject(Metadata *metadata, const void *x, const void *y) {
   if (!metadata || !y)
     return false;
 
-  return (GetMetadata(y) == x);
+  return (GetMetadata(y) == metadata);
 }
 
 u8 GetRefCount(Metadata *metadata) { return metadata->GetRefCount(); }