jimtcl: update embedded jimtcl

Update to latest jimtcl commit 2c1eba991e21a6f0b531fb0f83e21f9e6ee7c515.
This fixes issues when building on certain versions of Mac OSX.

Change-Id: I551477752d7913c84e6deb60b889d0c14bd200a0
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/1311
Tested-by: jenkins
Reviewed-by: Xiaofan <xiaofanc@gmail.com>