[std] Fix awk not finding default scripts

[kylewlacy]

GNU awk comes with a number of built-in scripts (e.g. calling gawk -i inplace uses a default script for in-place editing of a file). awk provided by Brioche doesn't work with these scripts currently.

This can probably be solved by setting $AWKPATH, see the docs here: https://www.gnu.org/software/gawk/manual/html_node/AWKPATH-Variable.html