* lib/intprops.h: Improve and shorten commentary.
For the record, if we ever run into a pedantic compiler that
behaves differently from GCC when converting an out-of-range value
to a signed integer, we can work around the problem with something
like the following code, where UCT is the signed counterpart of T
(UCT is sometimes narrower than UT) and all callers are changed
accordingly:
((t) ((ut) (a) op (ut) (b)))
(TYPE_MINIMUM (t) <= (uct) ((ut) (a) op (ut) (b)) \
? ((t) (uct) (((ut) (a) op (ut) (b)) - TYPE_MINIMUM (t)) \
+ TYPE_MINIMUM (t)) \
: (t) (uct) ((ut) (a) op (ut) (b)))