jimtcl: update to master branch 20210715

This version of jimtcl:
- fixes memory leak in API Jim_CreateCommand();
- fixes 'make distcheck';
- uses single-argument syntax for 'expr'.

With the 'expr' syntax already fixed in all the tcl scripts in
OpenOCD, let's use the latest jimtcl to check it and anticipate
any further issues.
By using this version, the workaround for the memory leak and for
distcheck can be reverted.

Change-Id: I58e1bdc752a728f1b479de1c55067b698e817ef5
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6226
Reviewed-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-by: zapb <dev@zapb.de>
Tested-by: jenkins

diff --git a/jimtcl b/jimtcl
index fb923fab4f0cf276c336d98692d00df6a943791d..2d66360c61d2a89d4008e8bad12ae3aa5f0331e2 160000 (submodule)
--- a/jimtcl
+++ b/jimtcl
@@ -1 +1 @@
-Subproject commit fb923fab4f0cf276c336d98692d00df6a943791d
+Subproject commit 2d66360c61d2a89d4008e8bad12ae3aa5f0331e2