sh: fix vsyscall compilation due to .eh_frame issue

This patch fixes the following error obtained when
compile the Kernel with the VSYSCALL support enabled:

  SYSCALL arch/sh/kernel/vsyscall/vsyscall-trapa.so
  sh4-linux/bin/ld: error in arch/sh/kernel/vsyscall/vsyscall-trapa.o(.eh_frame);
  no .eh_frame_hdr table will be created.
  AS      arch/sh/kernel/vsyscall/vsyscall-syscall.o

Disassembling the vsyscall-trapa.o code, with this fix applied,
we get the __kernel_vsyscall symbol defined; otherwise it was
missing.

Disassembly of section .text:

00000000 <__kernel_vsyscall>:
   0:	10 00       	.word 0x0010
   2:	00 00       	.word 0x0000
[snip]
0000040 <__kernel_sigreturn>:
  40:	05 93       	mov.w	4e <__kernel_sigreturn+0xe>,r3	! 77
  42:	10 c3       	trapa	#16
[snip]

00000060 <__kernel_rt_sigreturn>:
  60:	05 93       	mov.w	6e <__kernel_rt_sigreturn+0xe>,r3	! ad
  62:	10 c3       	trapa	#16
[snip]

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Reviewed-by: Carmelo Amoroso <carmelo.amoroso@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>