Use innermost builder cause to trim stack trace (#1380) (#1381)

Change the logic for determining which nested ChiselException cause to
use for a trimmed stack trace. Previously, this would use the
outermost. This commit changes this to use the innermost.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>
(cherry picked from commit 5d269ce3

)

Co-authored-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>