gdb-cross: Adjust ${datadir} to avoid file conflicts in sysroot

gdb-cross: Adjust ${datadir} to avoid file conflicts in sysroot

GDB wants to install a bunch of files in ${datadir}/gdb/python/gdb
and ${datadir}/gdb/syscalls.  These pathnames are invariant with
TARGET_ARCH which means that if you build gdb multiple times for
different targets they will all try to write to the same location
and you get a lot of warning spew about manifest conflicts.

Prevent this by factoring the target specification into ${datadir}
so that different copies of GDB install their files into different
paths.

(From OE-Core rev: 3e87aba1ee2ca0e39ba66fb7cba52e48df499c23)

Signed-off-by: Phil Blundell <philb@gnu.org>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>