guix-build: Add `--verbosity'.

* guix-build.in (%default-options): Add `verbosity'.
  (%options): Add `--verbosity'.
  (guix-build): Pass it to `set-build-options'.
  (show-help): Update accordingly.
* doc/guix.texi (Invoking guix-build): Document `--verbosity'.

1 files changed, 6 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index b8ab94f5ad..21f6d87b3a 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -532,6 +532,12 @@ value @code{0} means to use as many CPU cores as available.
 @itemx -r @var{file}
 Make @var{file} a symlink to the result, and register it as a garbage
 collector root.
+
+@item --verbosity=@var{level}
+Use the given verbosity level.  @var{level} must be an integer between 0
+and 5; higher means more verbose output.  Setting a level of 4 or more
+may be helpful when debugging setup issues with the build daemon.
+
 @end table
 
 Behind the scenes, @command{guix-build} is essentially an interface to