bug#8761: gnutls should use xmalloc not malloc

[Paul Eggert]

> I'm OK with the change, but how do I test that it behaves properly?

It's a bit hard to arrange for a test, since the thing you want
to try is to run gnutls when malloc fails.  Perhaps you can run
Emacs inside a debugger, and artificially arrange for malloc to
return NULL at exactly the right point.  But to be honest, I expect
that the old memory-failure code was never exercised, and that it's
low priority to test the new memory-failure code.