[TableGen] Fix both sides of '&&' are same

The operand of the second any_of in EnforceSmallerThan should be
B not S like the FP code in the if below.

Unfortunately, fixing that causes an infinite loop in the build
of RISCV. So I've added a workaround for that as well.

Fixes PR44768.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D111502