setarch: use a login shell; fixes #12066.

* This also updates /etc/profile to detect whether our
parent process is a shell, and changes the banner
message accordingly.
* Also, pipe errors to /dev/null, in case grep is not
installed; this allows us to not require grep as a
dependency, and let the banner message do the right
thing.

setarch: fix generation of new PATH environment variable.

* The insertion index didn't take into account the fact
that some paths don't get added before the index is
calculated. This resulted in the requested arch paths
ending up in reverse if we were already in the
requested arch environment.

Fixes #12125.

setarch: list available architectures

Signed-off-by: Oliver Tappe <zooey@hirschkaefer.de>

Add setarch and getarch commands

setarch: use a login shell; fixes #12066.

* This also updates /etc/profile to detect whether our
parent process is a shell, and changes the banner
message accordingly.
* Also, pipe errors to /dev/null, in case grep is not
installed; this allows us to not require grep as a
dependency, and let the banner message do the right
thing.

setarch: fix generation of new PATH environment variable.

* The insertion index didn't take into account the fact
that some paths don't get added before the index is
calculated. This resulted in the requested arch paths
ending up in reverse if we were already in the
requested arch environment.

Fixes #12125.

setarch: list available architectures

Signed-off-by: Oliver Tappe <zooey@hirschkaefer.de>

Add setarch and getarch commands