Add -default-to-nil-allocator flag (sets ODIN_DEFAULT_TO_NIL_ALLOCATOR)

src/build_settings.cpp

@@ -111,6 +111,7 @@ struct BuildContext {
 	String ODIN_ROOT;    // Odin ROOT
 	bool   ODIN_DEBUG;   // Odin in debug mode
 	bool   ODIN_DISABLE_ASSERT; // Whether the default 'assert' et al is disabled in code or not
+	bool   ODIN_DEFAULT_TO_NIL_ALLOCATOR; // Whether the default allocator is a "nil" allocator or not (i.e. it does nothing)
 
 	TargetEndianKind endian_kind;