Fix out-of-tree build

The current AX_CONFIG_SUBDIR_OPTION macro assumes that $srcdir is a
relative path. If it is not, jimtcl/configure.gnu is generated such that
an out-of-tree build will fail at the configure step unless the build dir
is a sibling to the source dir.

Change the generated jimtcl/configure.gnu wrapper to use the same
`dirname $0` trick as jimtcl/configure (which itself is a wrapper around
autosetup).

Change-Id: I0fb19ae114ba37169b422b28313262f9bd83eb6f
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/1528


Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-by: Xiaofan <xiaofanc@gmail.com>