poco: add patches to fix pcre link issue and library installation

This commit adds two patches for poco to fix two issues:

 - A link issue caused by the fact that Buildroot uses the "unbundled"
   mode for pcre, which is broken due to Poco poking into internal
   pcre symbols. A Gentoo patch is adapted to work around this
   problem.

 - A link and runtime issue caused by the fact that the shared
   libraries are simply not installed due to a bug in the Makefile. An
   upstream Poco commit is backported to solve this problem.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reported-by: Benno Schweikert <b.schweikert@prosystems.de>