/L_DOUBLE_SIZE=option
     /L_DOUBLE_SIZE=128 (D)

  Determines how the compiler interprets the long double type.  The
  qualifier options are 64 and 128.

  /L_DOUBLE_SIZE=64 treats all long double references as G_FLOAT,
  D_FLOAT, or T_FLOAT, depending on the value of the /FLOAT
  qualifier.

  /L_DOUBLE_SIZE=128 treats all long double references as X_FLOAT.