Mention __NHC__ alongside __HUGS__ and __HBC__ in the description
of the cpp symbol __GLASGOW_HASKELL__.
<para>(For reference: the comparable symbols for other
systems are:
<constant>__HUGS__</constant>
- for Hugs and
+ for Hugs,
+ <constant>__NHC__</constant>
+ for nhc98, and
<constant>__HBC__</constant>
for Chalmers.)</para>