contrib/buildsystems: handle quoted spaces in filenames

contrib/buildsystems: handle quoted spaces in filenames

The engine.pl script expects file names not to contain spaces. However,
paths with spaces are quite prevalent on Windows. Use shellwords() rather
than split() to parse them correctly.

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Philip Oakley <philipoakley@iee.org>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>