Label asconst and machdep arguments to avoid mixups

[sim642]

While reviewing things for #215, I noticed something odd: doExp has a bool argument meaning asconst, while constFold has one meaning machdep. In one place, the value of asconst is passed to be machdep:

cil/src/frontc/cabs2cil.ml

Line 5256 in 2243aad

CEExp (se, if !lowerConstants then constFold asconst e else e)

I find this strange: why should machdep be considered when converting to a constant, but not when converting a normal expression? This seems like a mixup.

To check this, I made both arguments labeled and indeed it's the only place this is mixed up like this.