Make sure the Tcl script does not stop if capnp emits a warning.
Make sure the Tcl script does not stop if capnp emits a warning.

The default Tcl exec has the unfortunate feature to fail when
the command in question outputs on stderr, switch this off.

Signed-off-by: Henner Zeller <259ad50fabbfd39355f36ecd6c0afca541ea66ef@acm.org>

chipsalliance/UHDM,chipsalliance/UHDM,chipsalliance/UHDM