POSIX <libintl.h> and restrict

[Bruno Haible]

https://posix.rhansen.org/p/gettext_draft
Lines 163..230, 538..543

The 'restrict' keywords in these declarations are useless and - worse -
forbid some valid, useful calls. For example, there is nothing wrong
with
   dgettext("hello", "hello")
which will attempt to search for a translation of "hello" in a catalog
name hello.mo. There is also no imaginable optimization that can be done
in the implementation of dgettext() by assuming that the two arguments
were different.

'restrict' is meaningful when at least one of the parameters is a
writable pointer type. Here, all parameters are either non-pointers
or read-only pointers.

Suggestion: Remove every 'restrict' in these declarations.