SIZEOF_SIZE_T doesn't exist on AIX, keep using SIZEOF_LONG

Follow up for 3689b44

Author: kaplanlior

ext/mbstring/oniguruma/regint.h

@@ -227,7 +227,11 @@
 } while(0)
 
 /* sizeof(OnigCodePoint) */
-#define WORD_ALIGNMENT_SIZE     SIZEOF_SIZE_T
+#ifdef SIZEOF_SIZE_T
+# define WORD_ALIGNMENT_SIZE     SIZEOF_SIZE_T
+#else
+# define WORD_ALIGNMENT_SIZE     SIZEOF_LONG
+#endif
 
 #define GET_ALIGNMENT_PAD_SIZE(addr,pad_size) do {\
   (pad_size) = WORD_ALIGNMENT_SIZE \