On my Debian Testing, the configure script recently started to not be able to execute ```source```. The only solution I found was be to replace ```#!/bin/sh``` by ```#!/bin/bash```.

The consequence of this is the display of the following messages:
```
$ xxx/bin/gpac
Unknown arch, cannot find executable path
Couldn't find GPAC binaries install directory
Unknown arch, cannot find executable path
Couldn't find GPAC binaries install directory
Unknown arch, cannot find executable path
Couldn't find GPAC binaries install directory
efreshing all options registry, this may take some time ... done
Nothing to do, check usage "gpac -h"
gpac - GPAC command line filter engine - version 1.1.0-DEV-revUNKNOWN-HEAD
(c) 2000-2021 Telecom Paris distributed under LGPL v2.1+ - http://gpac.io
```
configure: 'source' cannot be found in some /bin/sh
This is a GitHub Issue
repo:gpac
owner:gpac
Title : configure: 'source' cannot be found in some /bin/sh
Issue date:

--- start body ---
On my Debian Testing, the configure script recently started to not be able to execute ```source```. The only solution I found was be to replace ```#!/bin/sh``` by ```#!/bin/bash```.

The consequence of this is the display of the following messages:
```
$ xxx/bin/gpac
Unknown arch, cannot find executable path
Couldn't find GPAC binaries install directory
Unknown arch, cannot find executable path
Couldn't find GPAC binaries install directory
Unknown arch, cannot find executable path
Couldn't find GPAC binaries install directory
efreshing all options registry, this may take some time ... done
Nothing to do, check usage "gpac -h"
gpac - GPAC command line filter engine - version 1.1.0-DEV-revUNKNOWN-HEAD
(c) 2000-2021 Telecom Paris distributed under LGPL v2.1+ - http://gpac.io
```
--- end body ---
