log4cpp: new package

log4cpp: new package

Signed-off-by: Damien Lanson <damien@kal-host.com>
[Thomas:
 - Rewrap Config.in help text.
 - Add missing new line at the end of the Config.in help text.
 - Use 80 # signs for the .mk file header.
 - Use <pkg>_SUBDIR = log4cpp instead of moving things around during the
   extract step.
 - Fix typo in the license (it's LGPL, not GLPL), and make it LGPLv2.1+,
   since it's what the HTML documentation says.
 - In addition to removing the log4cpp-config script from the target,
   tweak the variant installed in staging so that it behaves properly
   for cross-compilation. Unfortunately, the <pkg>_CONFIG_SCRIPTS
   generic mechanism doesn't work for this config script.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>