Hide internal idna functions to allow direct access within libc.so and
libc.a without using GOT nor PLT.
[BZ #18822]
* include/idna.h: New file.
* inet/getnameinfo.c: Include <idna.h> instead of
<libidn/idna.h>.
(__idna_to_unicode_lzlz): Removed.
* sysdeps/posix/getaddrinfo.c: Include <idna.h> instead of
<libidn/idna.h>.
(__idna_to_ascii_lz): Removed.
(__idna_to_unicode_lzlz): Likewise.
