sh: Terminate .eh_frame in VDSO with a 4-byte 0.

It's assumed that .eh_frame is terminated with 4-byte 0 in shared
libraries and executable.  It seems to be the case for VDSOs too.
Without this terminator, I saw failures when unwinding from VDSO,
though I don't know how other architectures handle this issue.
For the normal libs, crtendS.o gives this terminator.  We can use
such terminating objects.  Or we can add a 4-byte 0 with modifying
the linker script like as the patch below.

Signed-off-by: Kaz Kojima <kkojima@rr.iij4u.or.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>