Fix the the case where src1 is constant and src2 is non-constant causing
an assert due to trying to call `.constant()` on the src2 operand.
Interfaces with an issue Gliniak was encountering where title `4D53082D`
encounters an assert. Also includes a BMI1-acceleration in the 64-bit
case where a temporary register is needed(the `and` x86 instruction only
supports immediate constants up to 32-bits).
4303f6b200