build: provide SIZEOF_SIZE_T definition for non-configure builds

config-dos.h

@@ -32,6 +32,7 @@
 #define RETSIGTYPE             void
 #define SIZEOF_INT             4
 #define SIZEOF_SHORT           2
+#define SIZEOF_SIZE_T          4
 #define TIME_WITH_SYS_TIME     1
 
 /* Qualifiers for send(), recv(), recvfrom() and getnameinfo(). */

config-win32.h

@@ -227,6 +227,13 @@
 /* The size of `short', as computed by sizeof. */
 #define SIZEOF_SHORT 2
 
+/* The size of `size_t', as computed by sizeof. */
+#if defined(_WIN64)
+#  define SIZEOF_SIZE_T 8
+#else
+#  define SIZEOF_SIZE_T 4
+#endif
+
 /* ---------------------------------------------------------------- */
 /*                          STRUCT RELATED                          */
 /* ---------------------------------------------------------------- */