Replace _DEBUG with Z3DEBUG (#7628)

Fixes #7627

Author: carsonRadtke

src/util/memory_manager.h

@@ -75,7 +75,7 @@ class memory {
 };
 
 
-#if _DEBUG
+#if Z3DEBUG
 
 #define alloc(T,...) new (memory::allocate(__FILE__,__LINE__,#T, sizeof(T))) T(__VA_ARGS__)
 #define dealloc(_ptr_) deallocf(__FILE__,__LINE__,_ptr_)