- compare_{le,lt)(): Use float64_{le,lt}_quiet() to avoid raising
  exceptions on QNaNs.
- alpha_fp_interpret(): Instructions are 32-bits wide, so don't use a
  uint64_t to contain them.
- alpha_fp_complete(): Operations on NaNs trap on Alpha, but the exception
  summary reports INV (invalid operation) rather than SWC (software
  completion) in this case.  So also interpret the instruction if INV
  is set in the exception summary.  This will emulate operations on
  NaN and correctly suppress FP traps for QNaNs.

This fixes bin/55633, which was caused by:

  -> Input string "nanotime" is passed to awk's internal is_number().
  -> strtod() interprets as "nan" and returns QNaN as the result.
  -> Result compared against HUGE_VAL, blows up because cmptle is called
    with a NaN operand, and the hardware doesn't care that it's quiet.

(thorpej)