Add xscale debug helper sources and everything related to dist

Add xscale debug helper sources and everything related to dist

GPL requires providing sources for any derived work. I do not see any
reason to not include the xscale stuff into release tarballs.

Wildcard matching is used because plain directory name matches
implicit rule for executables and xscale.c built is errorneously
attempted, and directory name with a slash duplicates a directory
(xscale/xscale) in dist.

Change-Id: Ie0266470dcb97be87a09ba2dda9b3957f7cbc2fa
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/1911
Tested-by: jenkins
Reviewed-by: Robert Jarzmik <robert.jarzmik@free.fr>
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>