Fix hard-coded path to /bin/bash -> /usr/bin/env bash
Fix hard-coded path to /bin/bash -> /usr/bin/env bash

On Posix systems, the path /bin/bash is not guaranteed to
exist and it is more portable to use /usr/bin/env instead.

Fixing this for yosys-config with is the most important for
a functioning installation.

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

YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys,YosysHQ/yosys