gnu: dlib: Update to 19.7.

* gnu/packages/machine-learning.scm (dlib): Update to 19.7.
[arguments]: Add #:configure-flags.  Remove redundant CXXFLAGS from 'check' phase.

gnu/packages/machine-learning.scm

@@ -524,14 +524,14 @@ (define-public r-kernlab
 (define-public dlib
   (package
     (name "dlib")
-    (version "19.3")
+    (version "19.7")
     (source (origin
               (method url-fetch)
               (uri (string-append
                     "http://dlib.net/files/dlib-" version ".tar.bz2"))
               (sha256
                (base32
-                "0gfy83av717qymv53yv7ki6mgh6mdw4xcxxbjk8lrs72f8qvnrcw"))
+                "1mljz02kwkrbggyncxv5fpnyjdybw2qihaacb3js8yfkw12vwpc2"))
               (modules '((guix build utils)))
               (snippet
                '(begin
@@ -541,7 +541,11 @@ (define-public dlib
                   #t))))
     (build-system cmake-build-system)
     (arguments
-     `(#:phases
+     ;; Recent releases defaults to "lib64" on 64bit.
+     `(#:configure-flags (list (string-append "-DCMAKE_INSTALL_LIBDIR="
+                                              (assoc-ref %outputs "out")
+                                              "/lib"))
+       #:phases
        (modify-phases %standard-phases
          (add-after 'unpack 'disable-asserts
            (lambda _
@@ -576,7 +580,6 @@ (define-public dlib
              ;; No test target, so we build and run the unit tests here.
              (let ((test-dir (string-append "../dlib-" ,version "/dlib/test")))
                (with-directory-excursion test-dir
-                 (setenv "CXXFLAGS" "-std=gnu++11")
                  (and (zero? (system* "make" "-j" (number->string (parallel-job-count))))
                       (zero? (system* "./dtest" "--runall")))))))
          (add-after 'install 'delete-static-library