cpplib: Stricter syntax checking

[Neil Booth]

Zack Weinberg wrote:-

> I only want this done if -pedantic is on.  And you're not checking for
> it anywhere but #define; it's forbidden everywhere but variadic macro
> expansions - but I wouldn't worry too much about it.  (I'm tempted to
> file a Defect Report on these semantics, they're awful.)

OK, I'd not insisted on pedantic since I imagine it's easy to get
confused if you go around #define-ing it or using it as an argument.

I read the standard as only referring to #define lines; I find that
item very confusing.

Later on in development, partic. when we merge with front-ends, we're
probably going to want to insert entries into the hash table early,
for things like __VA_ARGS__ and various keywords etc.  For one thing,
it saves the awkward string comparisons, which just become a pointer
comparison.  It would make checking for __VA_ARGS__ everywhere easier,
too, assuming that's what we want.

Neil.