Reported by Mark Ogden <mark@ogdens.plus.com>:

Sometime ago I noticed another bug in the fortran cross compiler. If you
look at plm81.for line 489, you will see a calculation:

PRMASK(I)=2**(I*8-8)-1

When I = 5 this becomes
PRMASK(I)=2**(5*8-8)-1
i.e.
PRMASK(5)=2**(32)-1

With 32 bit integers this causes overflow. Some fortran compilers complain
about this.

On 2's complement machines PRMASK(5) = -1 works without overflow.
