classes/package: reduce dbg package dependencies

Make dbg package dependencies added via DEPCHAIN_POST less aggressive -
only add dependencies on dbg packages for shared library dependencies.
This avoids dragging in extraneous packages (such as eglibc-dbg forcing
bash-dbg to be installed) whilst preserving the ability to easily debug
into shared libraries in use by an application by just requesting the
installation of the single dbg package for that application.

For task recipes however we preserve the previous behaviour, since when
you install task-xxx-dbg you expect the dbg packages for every package
in the task to be installed. Unfortunately not all of our tasks inherit
from task.bbclass so we just use a name match - this should be tidied up
later.

Fixes [YOCTO #2599].

(From OE-Core rev: 352522d474cb75992d7865545b6fbe4e157a5f99)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/task.bbclass

@@ -25,3 +25,6 @@ python () {
     d.setVar('PACKAGES', ' '.join(packages+genpackages))
 }
 
+# We don't want to look at shared library dependencies for the
+# dbg packages
+DEPCHAIN_DBGDEFAULTDEPS = "1"