gdb: build with expat, add missing RRECOMMENDS_gdbserver

gdb: build with expat, add missing RRECOMMENDS_gdbserver

* Fixes communication between gdbserver and gdb-cross
  by using the same expat settings for both recipes.
* Adds missing build dependencies for expat/expat-native.
* Adds missing glibc-thread-db runtime recommendation
  to gdbserver, which was set only for gdb.

(From OE-Core rev: 38ee88e3b32b7444d7f1eb64f1b4f69a48fe0458)

Signed-off-by: Andreas Oberritter <obi@opendreambox.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>