librtas: new package

[Thomas:
  - make the package depend on glibc, since it needs execinfo.h
  - use TARGET_CONFIGURE_OPTS instead of defining manually CC and LD
  - add hash file
  - remove useless empty newline.
  Thanks to Romain Naour for the review!]

Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
Reviewed-by: Romain Naour <romain.naour@openwide.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>