Make USECS_PER_* timestamp macros visible even when we are not using

integer timestamps.

src/include/utils/timestamp.h

@@ -93,12 +93,10 @@ typedef struct
 #define SECS_PER_MINUTE 60
 #define MINS_PER_HOUR	60
 
-#ifdef HAVE_INT64_TIMESTAMP
 #define USECS_PER_DAY	INT64CONST(86400000000)
 #define USECS_PER_HOUR	INT64CONST(3600000000)
 #define USECS_PER_MINUTE INT64CONST(60000000)
 #define USECS_PER_SEC	INT64CONST(1000000)
-#endif
 
 /*
  * Macros for fmgr-callable functions.