json: Add stpcpy replacement.
json: Add stpcpy replacement.

* src/gpgme-json.c [!HAVE_STPCPY](_my_stpcpy): New.

Signed-off-by: Werner Koch <13bd1fc5137f503b0a8355ad400e7a87ebb45b25@gnupg.org>

gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme