jimtcl: update to tag 0.79

OpenOCD is stuck at jimtcl tag 0.77 that is 3 years old.
The latest tag 0.79 (2019-11-20) is already used by debian build,
which packs jim library separately, as shown in [1]. Today only
the build for architecture powerpcspe is still not updated to
latest package version.
I have been using jim 0.79 since the day of the release, without
any issue.

Switch jimtcl to latest tag 0.79

[1] https://packages.debian.org/sid/openocd

Change-Id: I3426e68c32f88ecde74d4278303925423db451e0
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5403
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

diff --git a/jimtcl b/jimtcl
index a9bf5975fd0f89974d689a2d9ebd0873c8d64787..0aa0fb4e3a38d38a49de9eb585d93d63a370dcf6 160000 (submodule)
--- a/jimtcl
+++ b/jimtcl
@@ -1 +1 @@
-Subproject commit a9bf5975fd0f89974d689a2d9ebd0873c8d64787
+Subproject commit 0aa0fb4e3a38d38a49de9eb585d93d63a370dcf6