jim: update to fix mingw/msys build issues

Signed-off-by: Spencer Oliver <ntfreak@users.sourceforge.net>

diff --git a/jimtcl b/jimtcl
index 6233a6c5d39928f1bfafa8f41cb1ddf0c5a83de0..645ed6fd4b6f9038c7e1d85d74c3872b3cb9a507 160000 (submodule)
--- a/jimtcl
+++ b/jimtcl
@@ -1 +1 @@
-Subproject commit 6233a6c5d39928f1bfafa8f41cb1ddf0c5a83de0
+Subproject commit 645ed6fd4b6f9038c7e1d85d74c3872b3cb9a507