[Bug c/114526] ISO C does not prohibit extensions: fix misconception.

[jsm28 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114526

--- Comment #5 from Joseph S. Myers <jsm28 at gcc dot gnu.org> ---
The -pedantic documentation was updated to reflect reality - that the option is
about more than just when diagnostics are required by ISO C ("forbidden
extensions" can be taken, in the C case, as meaning those that involve
constraint violations or are outside the standard C syntax) but covers some
other programs doing things not defined in ISO C as well - in commit
074e95e34275d72664f997ed949d9c91e37cd6ee (July 2000). I don't think any
possible narrower intent there may have been long before then is particularly
relevant now.

It may well be the case that for certain diagnostics for things that do not
violate constraints or syntax rules, "ISO C does not define" or "is a GNU
extension" or similar would be better wording.