benchmarks/uica: fix build on riscv and in UTC-... time zones

 - inform mbuild CPU type detection script about the
   existence of this newfangled architecture.
 - pass TZ=UTC to date(1) while generating distfile name
   to avoid off by one error on the first day of the month
   in time zones west of Greenwich.

PR:		267020
Submitted by:	maintainer
MFH:		2022Q4