Fix objtool configure check

The m4 objtool configure check can incorrectly fail because of a
missing header in the test. This appears to be the result of a
recent kernel change and was observed on the Fedora 5.8.11-200
kernel.

  In file included from /home/fedora/zfs/build/objtool/objtool.c:75:
  ./arch/x86/include/asm/frame.h:100:57: error: 'struct pt_regs'
      declared inside parameter list will not be visible outside
      of this definition or declaration [-Werror]

The consequence of this is that the "stack_frame_non_standard"
check is never run and HAVE_STACK_FRAME_NON_STANDARD is set
incorrectly which results in a build failure. This change adds
the appropriate header to the "objtool" check so it now behaves
as intended.

Reviewed-by: Kjeld Schouten <kjeld@schouten-lebbing.nl>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #10990