objtool: Fix cross-build

Stephen Rothwell reported this cross-compilation build failure:

| In file included from orc_dump.c:19:0:
| orc.h:21:10: fatal error: asm/orc_types.h: No such file or directory
| ...

Caused by:

  6a77cff8 ("objtool: Move synced files to their original relative locations")

Use the proper arch header files location, not the host-arch location.

Bisected-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux-Next Mailing List <linux-next@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20171108030152.bd76eahiwjwjt3kp@treble


Signed-off-by: Ingo Molnar <mingo@kernel.org>