scripts: Add --list-systems and --list-targets options.

Also factorize the --system and --target build options. Check that the passed
system and target arguments are known platforms.

* doc/guix.texi (Additional Build Options): Document the new --list-systems
and --list-targets options.
* guix/scripts/build.scm (show-cross-build-options-help,
show-emulated-build-options-help, list-systems, list-targets): New procedures.
(%standard-cross-build-options, %standard-emulated-build-options): New
variables.
(show-help): Remove --system and --target entries and use
show-cross-build-options-help and show-emulated-build-options-help procedures instead.
(%options): Remove --system and --target entries and use
%standard-cross-build-options and %standard-emulated-build-options variables instead.
* guix/scripts/archive.scm (show-help, %options): Adapt them.
* guix/scripts/environment.scm: Ditto.
* guix/scripts/graph.scm: Ditto.
* guix/scripts/pack.scm: Ditto.
* guix/scripts/pull.scm: Ditto.
* guix/scripts/size.scm: Ditto.
* guix/scripts/weather.scm: Ditto.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 9cdee15d55..761fceb9c3 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -12397,6 +12397,14 @@ Cross-build for @var{triplet}, which must be a valid GNU triplet, such
 as @code{"aarch64-linux-gnu"} (@pxref{Specifying Target Triplets, GNU
 configuration triplets,, autoconf, Autoconf}).
 
+@item --list-systems
+List all the supported systems, that can be passed as an argument to
+@option{--system}.
+
+@item --list-targets
+List all the supported targets, that can be passed as an argument to
+@option{--target}.
+
 @anchor{build-check}
 @item --check
 @cindex determinism, checking