libpqxx: apply upstream compilation fix

libpqxx: apply upstream compilation fix

Apply an upstream patch which addresses a compilation issue with respect
to an undefined 'timeval' structure. This issue exists in at least v6.0.
It is expected that this patch can be removed when libpqxx provides a
new releases (either v6.0.1 or v6.1).

Fixes:
http://autobuild.buildroot.net/results/48b015650ede4e55e199538072c7228cccf64422

Signed-off-by: James Knight <james.knight@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>