export_report: do collectcfiles work in perl itself

Avoid spawning a shell pipeline doing cat, grep, sed, and do it all
inside perl.  The <*.c> globbing construct works at least as far back
as 5.8.9

Note that this is not just an optimization; the sed command
in the pipeline was unterminated, due to lack of escape on the
end-of-line (\$) in the regex, resulting in this:

    $ perl ../linux-2.6/scripts/export_report.pl  > /dev/null
    sed: -e expression #1, char 5: unterminated `s' command
    sh: .mod.c/: not found

Comments on an earlier patch sought an all-perl implementation.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
cc: Michal Marek <mmarek@suse.cz>,
cc: linux-kbuild@vger.kernel.org
cc: Arnaud Lacombe lacombar@gmail.com
cc: Stephen Hemminger shemminger@vyatta.com
Signed-off-by: Michal Marek <mmarek@suse.cz>