[yocto] Add new module to recipe + meta-toolchain-qt: add gdb

[Jose Mª Ferreiro]

Hello

We have compiled meta-toolchain-qt (Yocto dylan). Now we can run QT 
applications on Desktop (Ubuntu 12.04) and on target (iMX6 sabre Lite 
board). We can also debug the applications on board, but we can not 
debug on desktop.

When /usr/bin/gdb is started it starts automatically /usr/bin/python. It 
fails because Ubuntu python does not recognize sys.lib variable from 
/op/poky...python. We have found no way to tell gdb to start changing 
PYTHONHOME to Ubuntu python home to avoid the problem.

So we need to add gdb to the toolchain. If we get it to work, we suppose 
the /op/poky...gdb will start the /opt/poky...python (we test it and 
that python knows what sys.lib is).

We try to add to conf/local.conf: TOOLCHAIN_HOST_TASK_append = " 
nativesdk-gdb". But nativesdk-gdb is not a defined name.

So the cuestion is: how can i know what recipes are avaliable to sdk 
host toolchain and what are their names?

Thank you and best regards