When config_host.mk contains non-ascii characters(e.g. Japanese ),
SRC_ROOT may contain an error message "Binary file (standard input)
 matches") from grep, and SRC_ROOT may not contain path string.
With '-a' option, grep will work well.

Change-Id: Ifaada5f5a11939d624460cd8dcc57d93911ae790
Reviewed-on: https://gerrit.libreoffice.org/14491Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>