InnoDB: Fix debug compile error on Tru64 (Bug #8244)

innobase/include/rem0rec.ic:
  Eliminate int16_t from an assertion, as it is not defined in the
  same system headers on all platforms.  (Bug #8244)

innobase/include/rem0rec.ic

@@ -279,7 +279,15 @@ rec_get_next_offs(
 		/* Note that for 64 KiB pages, field_value can 'wrap around'
 		and the debug assertion is not valid */
 
-		ut_ad((int16_t)field_value
+		/* In the following assertion, field_value is interpreted
+		as signed 16-bit integer in 2's complement arithmetics.
+		If all platforms defined int16_t in the standard headers,
+		the expression could be written simpler as
+		(int16_t) field_value + ut_align_offset(...) < UNIV_PAGE_SIZE
+		*/
+		ut_ad((field_value >= 32768
+			? field_value - 65536
+			: field_value)
 		       + ut_align_offset(rec, UNIV_PAGE_SIZE)
 		      < UNIV_PAGE_SIZE);
 #endif