gnu: Build wiredtiger with snappy support.

This is probably necessary to get the MongoDB package in Guix to successfully
use the Guix wiredtiger package, as MongoDB it uses wiredtiger with snappy by
default.

* gnu/packages/databases.scm (wiredtiger)[arguments]: Add --enable-snappy to
  #:configure-flags.
  [inputs]: Add snappy.

gnu/packages/databases.scm

@@ -1500,7 +1500,7 @@ organized in hash table, B+ tree, or fixed-length array.")
                 "0krwnb2zfbhvjaskwl875qzd3y626s84zcciq2mxr5c5riw3yh6s"))))
     (build-system gnu-build-system)
     (arguments
-     '(#:configure-flags '("--enable-lz4" "--enable-zlib")
+     '(#:configure-flags '("--enable-lz4" "--enable-zlib" "--enable-snappy")
        #:phases
        (modify-phases %standard-phases
          (add-before 'check 'disable-test/fops
@@ -1511,7 +1511,8 @@ organized in hash table, B+ tree, or fixed-length array.")
              #t)))))
     (inputs
      `(("lz4" ,lz4)
-       ("zlib" ,zlib)))
+       ("zlib" ,zlib)
+       ("snappy" ,snappy)))
     (home-page "http://source.wiredtiger.com/")
     (synopsis "NoSQL data engine")
     (description