new syscall stub support for ia64 libc

[David Mosberger]

>>>>> On Mon, 8 Dec 2003 20:09:58 +0100, Jakub Jelinek <jakub@redhat.com> said:

  Jakub> In 2.4.x kernels the signal trampoline indeed lived between
  Jakub> 0xa000000000010000 and 0xa000000000020000, but with the VDSO
  Jakub> changes it now is at 0xa0000000000207e0 though.

It occurred to me that another (much simpler) approach would be to
simply remove the guard-page and then move the DSO mappings down by
64KB.  The combination of READONLY and EXECUTEONLY DSO mappings should
have the same effect as the single NOPROT guard-page, so it's not
strictly needed anymore.

	--david