process-util: don't use overly large buffer to store process command line

process-util: don't use overly large buffer to store process command line

Allocate new string as a return value and free our "scratch pad"
buffer that is potentially much larger than needed (up to
_SC_ARG_MAX).

Fixes #11502

(cherry picked from commit eb1ec489eef8a32918bbfc56a268c9d10464584d)

Gbp-Pq: Name process-util-don-t-use-overly-large-buffer-to-store-proce.patch