RoundMode in ISA_Decls conflicts with that in FloatingPoint.bsv

[jonwoodruff]

ISA_Decls.bsv has a RoundMode enumerated type that appears to have a similar function but be different than the one in FloatingPoint.bsv. Due to some unknown priority effect this apparently has not been causing build failures, but the up-to-date BSC falls over due to the confusion. Things appear to build ok RoundMode in ISA_Decls is simply deleted.

[quark17]

This was also discussed at B-Lang-org/bsc#329