libc-common: Allow -dbg package to append, and not just set package variables

libc-common: Allow -dbg package to append, and not just set package variables

The libc-common attempts to rewrite the package information in a way similar
to debian.bbclass.  When it does this, it should be appending to the
dependency variables (RPROVIDES, RREPLACES, and RCONFLICTS), instead
of simply setting a hard coded value.  Otherwise the lib package can not
tailor the dependency variables to suite it's needs.

(From OE-Core rev: fa1c7b797593cbd5e82dc264bde2667620eb0515)

Signed-off-by: Mark Hatle <mark.hatle@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>