gnu: cereal-1.3.0: Update doctest.h.

* gnu/packages/serialization.scm (cereal-1.3.0)[native-inputs]: Add gcc-10 and
the sources of the cereal package.
[arguments]: Add a phase to replace the included doctest.h with the variant
from the cereal sources; disable -Werror.
[source]: Delete included doctest.h.

gnu/packages/serialization.scm

@@ -195,17 +195,26 @@ such as compact binary encodings, XML, or JSON.")
        (file-name (git-file-name "cereal" version))
        (sha256
         (base32
-         "0hc8wh9dwpc1w1zf5lfss4vg5hmgpblqxbrpp1rggicpx9ar831p"))))
+         "0hc8wh9dwpc1w1zf5lfss4vg5hmgpblqxbrpp1rggicpx9ar831p"))
+       (snippet
+        '(delete-file "unittests/doctest.h"))))
     (arguments
      (substitute-keyword-arguments (package-arguments cereal)
        ((#:configure-flags flags #~'())
-        #~'("-DSKIP_PORTABILITY_TEST=ON"))
+        #~'("-DSKIP_PORTABILITY_TEST=ON" "-DWITH_WERROR=OFF"))
        ((#:phases phases #~%standard-phases)
         #~(modify-phases #$phases
+            (add-after 'unpack 'update-doctest
+              (lambda* (#:key inputs #:allow-other-keys)
+                (install-file (search-input-file inputs "unittests/doctest.h")
+                              "unittests/")))
             (add-before 'configure 'skip-sandbox
               (lambda _
                 (substitute* "CMakeLists.txt"
-                  (("add_subdirectory\\(sandbox\\)") ""))))))))))
+                  (("add_subdirectory\\(sandbox\\)") ""))))))))
+    (native-inputs
+     (list doxygen gcc-10
+           (package-source cereal)))))
 
 (define-public msgpack
   (package