Add and use a macro to define placement-new-only allocators

This is for structs that utilize over-allocation, either flexible array
members, or which store optional additional objects in the same allocation
block.

Alc/mastering.h

@@ -61,9 +61,7 @@ struct Compressor {
     ALfloat LastAttack;
     ALfloat LastGainDev;
 
-    void *operator new(size_t size) = delete;
-    void *operator new(size_t /*size*/, void *ptr) noexcept { return ptr; }
-    void operator delete(void *block) noexcept { al_free(block); }
+    DEF_PLACE_NEWDEL()
 };
 
 /* The compressor is initialized with the following settings:

common/almalloc.h

@@ -31,6 +31,10 @@ int al_is_sane_alignment_allocator(void) noexcept;
     }                                                                         \
     void operator delete(void *block) noexcept { al_free(block); }
 
+#define DEF_PLACE_NEWDEL()                                                    \
+    void *operator new(size_t /*size*/, void *ptr) noexcept { return ptr; }   \
+    void operator delete(void *block) noexcept { al_free(block); }
+
 namespace al {
 
 template<typename T, size_t alignment=DEF_ALIGN>