frv minmax predicate

[DJ Delorie]

The minmax_operator predicate also checks the operands of the operator
to be appropriate, but the minmax_operator predicate is used for both
integer and floating point operations.  The predicate, as is, only
matches the integer operands.

Taking out the check on XEXP(...) in minmax_operator seems to get
around the ICE we're seeing, but is this the right thing to do?  Or do
we need separate predicates for integer vs floating point?