derivations: Avoid uses of 'write' in 'write-derivation'.

This leads a 4% improvement on the wall-clock time of:

  guix build -e '(@@ (gnu packages libreoffice) libreoffice)' --no-grafts -d

* guix/derivations.scm (escaped-string): New procedure.
(write-derivation)[write-escaped-string]: New procedure.
[write-string-list, write-output, write-env-var]: Use it.

0 files changed, 0 insertions, 0 deletions