package/boost: add library coroutine2

Coroutine2 is a new (C++14) library added in boost 1.59.0. We also add
coroutine2 to the '--without-libraries' configuration flag for the host
variant.

Build successfully tested with Arago ARMv5 2011.09 - a gcc v4.5.3 toolchain.

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Reviewed-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Tested-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>