k. Array/Object recursion protection
l. HASH_FLAG_PERSISTENT
m. AST and IS_CONSTANT
+ n. GC_REFCOUNT()
2. Build system changes
a. Unix build system changes
attributes are used instead of constant flags. IS_TYPE_CONSTANT flag is
removed, but Z_CONSTANT() macro is kept for compatibility.
+ m. GC_REFCOUNT() is turned into inline function and can't be modified direcly.
+ All reference-counting operations should be done through corresponding
+ macros GC_SET_REFCOUNT(), GC_ADDREF() and GC_DELREF().
+
+ GC_REFCOUNT(p)++ should be changed into GC_ADDREF(p),
+ GC_REFCOUNT(p)-- into GC_DELREF(p),
+ GC_REFCOUNT(p) = 1 into GC_SET_REFCOUNT(p, 1).
+
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2. Build system changes
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