LU-1337 build: fix build on powerpc64

LU-1337 build: fix build on powerpc64

Previous LU-1337 commit ca512093cd29e79ff8a43d4cd921058163305784
broke the build on powerpc64 by changing the way system type is
looked up, but failing to adjust the sed pattern to match the
$target_cpu name.

Change-Id: Ie0c8166f80c5361a8e89ab447c2025a31824914d
Signed-off-by: Christopher J. Morrone <morrone2@llnl.gov>
Reviewed-on: http://review.whamcloud.com/4149
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>