Adjust code so that CMUCL can use arrays to store quad-doubles instead

of using a (complex double-double-float).

With these changes, CMUCL uses arrays and (rt:do-tests) passes
successfully.

oct.system:
o Push :oct-array onto *FEATURES* to use arrays.  This is the default
  if not building on CMUCL.

qd-fun.lisp:
o Fix two erroneous uses of zerop on a quad-double in sinh-qd and
  tanh-qd.
o Fix two erroneous uses of + on %quad-double; they should have used
  ADD-QD instead.

qd-rep.lisp:
o Change conditionalization to allow arrays for CMUCL.
o Update compiler macros appropriately.

qd.lisp:
o Adjust optional target arg appropriately for oct-array feature.
o Clean up IGNORE declarations.
o Add some more declarations for the target to make CMUCL happier.