build-system/gnu: Honor the patch-shebangs?' and strip-binaries?' parameters.

* guix/build/gnu-build-system.scm (patch-shebangs): Honor
  PATCH-SHEBANGS?.
  (strip): Honor STRIP-BINARIES?.  Display a message from `strip-dir'.

guix/build/gnu-build-system.scm

@@ -152,13 +152,14 @@
                         (string-append dir "/sbin"))))
                 outputs))
 
+  (when patch-shebangs?
     (let ((path (append bindirs
                         (search-path-as-string->list (getenv "PATH")))))
       (for-each (lambda (dir)
                   (let ((files (list-of-files dir)))
                     (for-each (cut patch-shebang <> path) files)))
-             bindirs)
-   #t))
+                bindirs)))
+  #t)
 
 (define* (strip #:key outputs (strip-binaries? #t)
                 (strip-flags '("--strip-debug"))
@@ -166,6 +167,8 @@
                                      "bin" "sbin"))
                 #:allow-other-keys)
   (define (strip-dir dir)
+    (format #t "stripping binaries in ~s with flags ~s~%"
+            dir strip-flags)
     (file-system-fold (const #t)
                       (lambda (path stat result)  ; leaf
                         (zero? (apply system* "strip"
@@ -181,6 +184,7 @@
                       #t
                       dir))
 
+  (or (not strip-binaries?)
       (every strip-dir
              (append-map (match-lambda
                           ((_ . dir)
@@ -188,7 +192,7 @@
                                          (let ((sub (string-append dir "/" d)))
                                            (and (directory-exists? sub) sub)))
                                        strip-directories)))
-                     outputs)))
+                         outputs))))
 
 (define %standard-phases
   ;; Standard build phases, as a list of symbol/procedure pairs.