cpu-x86: clear the x87 stack when rewinding; fixes math.floats.env failures on Linux
cpu-x86: clear the x87 stack when rewinding; fixes math.floats.env failures on Linux

mcandre/factor,littledan/Factor,mcandre/factor,littledan/Factor,seckar/factor,erg/factor,erg/factor,mcandre/factor,mcandre/factor,erg/factor,seckar/factor,mcandre/factor,cataska/factor,seckar/factor,littledan/Factor,ceninan/factor,erg/factor,cataska/factor,mcandre/factor,erg/factor,erg/factor,kingcons/factor,kingcons/factor,littledan/Factor,cataska/factor,cataska/factor,ceninan/factor,erg/factor,mcandre/factor,kingcons/factor,ceninan/factor,ceninan/factor,kingcons/factor