poppler: add patch to fix invalid syntax in configure script

When configuring poppler, a shell error occurs:

./configure: line 19741: test: x: unary operator expected

This is due to an invalid configure test, which is fixed by a newly
added patch. We patch the configure script directly because poppler
doesn't autoreconf properly. A patch on configure.ac has been
submitted upstream so that hopefully we can drop our patch in a future
release of poppler.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>