emacs: Add key bindings for 'guix-build-log-minor-mode'.

* emacs/guix-build-log.el (guix-build-log-mode-map): Move keys to ...
  (guix-build-log-common-map): ...here.  New variable.
  (guix-build-log-minor-mode-map): New variable.
  (guix-build-log-minor-mode): Use it.
* doc/emacs.texi (Emacs Build Log): Document it.

doc/emacs.texi

@@ -646,12 +646,13 @@ Toggle (show/hide) the bodies of all build phases.
 @end table
 
 There is also @kbd{M-x guix-build-log-minor-mode} which also provides
-the same highlighting (but not key bindings).  And as it is a minor
+the same highlighting.  And as it is a minor mode, it can be enabled in
-mode, it can be enabled in any buffer.  For example, if you are building
+any buffer.  For example, if you are building some package in a shell
-some package in a shell buffer (@pxref{Interactive Shell,,, emacs, The
+buffer (@pxref{Interactive Shell,,, emacs, The GNU Emacs Manual}), you
-GNU Emacs Manual}), you may enable @command{guix-build-log-minor-mode}
+may enable @command{guix-build-log-minor-mode} to make it more colorful.
-to make it more colorful.  Guix build output is rather specific, so this
+Guix build output is rather specific, so this new highlighting shouldn't
-new highlighting shouldn't conflict with the existing one.
+conflict with the existing one.  This mode also provides the same key
+bindings as the major mode, but prefixed with @kbd{C-c}.
 
 
 @node Emacs Completions

emacs/guix-build-log.el

@@ -178,9 +178,8 @@ STATE is a symbol denoting how a build phase was ended.  It should be
      (3 'guix-build-log-phase-seconds prepend)))
   "A list of `font-lock-keywords' for `guix-build-log-mode'.")
 
-(defvar guix-build-log-mode-map
+(defvar guix-build-log-common-map
   (let ((map (make-sparse-keymap)))
-    (set-keymap-parent map special-mode-map)
     (define-key map (kbd "M-n") 'guix-build-log-next-phase)
     (define-key map (kbd "M-p") 'guix-build-log-previous-phase)
     (define-key map (kbd "TAB") 'guix-build-log-phase-toggle)
@@ -188,8 +187,24 @@ STATE is a symbol denoting how a build phase was ended.  It should be
     (define-key map (kbd "<backtab>") 'guix-build-log-phase-toggle-all)
     (define-key map [(shift tab)] 'guix-build-log-phase-toggle-all)
     map)
+  "Parent keymap for 'build-log' buffers.
+For `guix-build-log-mode' this map is used as is.
+For `guix-build-log-minor-mode' this map is prefixed with 'C-c'.")
+
+(defvar guix-build-log-mode-map
+  (let ((map (make-sparse-keymap)))
+    (set-keymap-parent
+     map (make-composed-keymap (list guix-build-log-common-map)
+                               special-mode-map))
+    map)
   "Keymap for `guix-build-log-mode' buffers.")
 
+(defvar guix-build-log-minor-mode-map
+  (let ((map (make-sparse-keymap)))
+    (define-key map (kbd "C-c") guix-build-log-common-map)
+    map)
+  "Keymap for `guix-build-log-minor-mode' buffers.")
+
 (defun guix-build-log-phase-start (&optional with-header?)
   "Return the start point of the current build phase.
 If WITH-HEADER? is non-nil, do not skip 'starting phase ...' header.
@@ -319,9 +334,12 @@ When Guix Build Log minor mode is enabled, it highlights build
 log in the current buffer.  This mode can be enabled
 programmatically using hooks:
 
-  (add-hook 'shell-mode-hook 'guix-build-log-minor-mode)"
+  (add-hook 'shell-mode-hook 'guix-build-log-minor-mode)
+
+\\{guix-build-log-minor-mode-map}"
   :init-value nil
   :lighter " Guix-Build-Log"
+  :keymap guix-build-log-minor-mode-map
   :group 'guix-build-log
   (if guix-build-log-minor-mode
       (font-lock-add-keywords nil guix-build-log-font-lock-keywords)