objtool: Update sync-check.sh from perf's check-headers.sh

To allow using the -I trick that will be needed for checking the x86
insn decoder files.

Without the specific -I lines we still get the same warnings as before:

  $ make -C tools/objtool/ clean ; make -C tools/objtool/
  make: Entering directory '/home/acme/git/perf/tools/objtool'
    CLEAN    objtool
  find  -name '*.o' -delete -o -name '\.*.cmd' -delete -o -name '\.*.d' -delete
  rm -f arch/x86/inat-tables.c fixdep
  <SNIP>
    LD       objtool-in.o
  make[1]: Leaving directory '/home/acme/git/perf/tools/objtool'
  Warning: Kernel ABI header at 'tools/arch/x86/include/asm/inat.h' differs from latest version at 'arch/x86/include/asm/inat.h'
  diff -u tools/arch/x86/include/asm/inat.h arch/x86/include/asm/inat.h
  Warning: Kernel ABI header at 'tools/arch/x86/include/asm/insn.h' differs from latest version at 'arch/x86/include/asm/insn.h'
  diff -u tools/arch/x86/include/asm/insn.h arch/x86/include/asm/insn.h
  Warning: Kernel ABI header at 'tools/arch/x86/lib/inat.c' differs from latest version at 'arch/x86/lib/inat.c'
  diff -u tools/arch/x86/lib/inat.c arch/x86/lib/inat.c
  Warning: Kernel ABI header at 'tools/arch/x86/lib/insn.c' differs from latest version at 'arch/x86/lib/insn.c'
  diff -u tools/arch/x86/lib/insn.c arch/x86/lib/insn.c
  /home/acme/git/perf/tools/objtool
    LINK     objtool
  make: Leaving directory '/home/acme/git/perf/tools/objtool'
  $

The next patch will add the -I lines for those files.

Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: http://lore.kernel.org/lkml/20190830193109.p7jagidsrahoa4pn@treble
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/n/tip-vu3p38mnxlwd80rlsnjkqcf2@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>