<limits.h>: Several changes related to Issue 7 of the standard.

<limits.h>: Several changes related to Issue 7 of the standard.

* NL_NMAX was removed, so change its visibility accordingly.

* NL_ARGMAX, NL_MSGMAX, NL_SETMAX and NL_TEXTMAX were moved from XSI
  into the base. Adjust for that too. The change history does not
  mention NL_ARGMAX but the [XSI] margin code was removed from it so
  I think this is just an oversight.

The 32 ports that reference NL_NMAX, which is the only of these
defines where visibility was restricted with this commit, all still
build.