Use correct word width

--- a/src/postgres/include/pg_config.h
+++ b/src/postgres/include/pg_config.h
@@ -686,7 +686,12 @@
 #define SIZEOF_SIZE_T 8
 
 /* The size of `void *', as computed by sizeof. */
+#include <bits/wordsize.h>
+#if __WORDSIZE == 64
 #define SIZEOF_VOID_P 8
+#else
+#define SIZEOF_VOID_P 4
+#endif
 
 /* Define to 1 if you have the ANSI C header files. */
 #define STDC_HEADERS 1
