Please, use changelog format for changes in commit message.

See:

https://www.gnu.org/prep/standards/html_node/Change-Logs.html

-     (substitute-keyword-arguments (strip-keyword-arguments
-                                    (list #:tests?)
-                                    (package-arguments cbqn-bootstrap))
-       ((#:make-flags flags #~(list))
-        #~(cons* "shared-o3" "o3" #$flags))
-       ((#:phases phases #~%standard-phases)
+     (substitute-keyword-arguments (strip-keyword-arguments (list #:tests?)
+                                                            (package-arguments
+                                                             cbqn-bootstrap))
+       ((#:make-flags flags
+         #~(list))
+        #~(cons* "shared-o3" "o3"
+                 #$flags))
+       ((#:phases phases
+         #~%standard-phases)

Try to avoid unnecessary modifications in original code, this makes hard
to follow the contributions.

-                                         #+bqn-sources
-                                         "/test/this.bqn\""))
+                                         #+bqn-sources "/test/this.bqn\""))

Idem

-                (let* ((bin (string-append (assoc-ref outputs "out")
-                                           "/bin"))
-                       (lib (string-append (assoc-ref outputs "lib")
-                                           "/lib"))
+                (let* ((bin (string-append (assoc-ref outputs "out") "/bin"))
+                       (lib (string-append (assoc-ref outputs "lib") "/lib"))
                        (include (string-append (assoc-ref outputs "lib")
-                                           "/include")))
+                                               "/include")))

Again. You get the idea.