guix build: Factorize common options.
* guix/scripts/build.scm (show-build-options-help,
set-build-options-from-command-line): New procedures.
(show-help): Remove description of --dry-run,
--fallback, --no-substitutes, --max-silent-time, and --cores. Call
'show-build-options-help'.
(%standard-build-options): New variable.
(%options): Remove --dry-run, --fallback, --no-substitutes,
--verbosity, --max-silent-time, and --cores. Add
%STANDARD-BUILD-OPTIONS.
(guix-build): Use 'set-build-options-from-command-line' instead of
'set-build-options'.
* guix/scripts/archive.scm (show-help): Remove description of --dry-run,
--fallback, --no-substitutes, --max-silent-time, and --cores. Call
'show-build-options-help'.
(%options): Remove --dry-run, --fallback, --no-substitutes,
--verbosity, --max-silent-time, and --cores. Add
%STANDARD-BUILD-OPTIONS.
(export-from-store): Call 'set-build-options-from-command-line'
instead of 'set-build-options.