flatpak: Add cmocka dependency

org.gnome.Calls.json

@@ -134,6 +134,18 @@
                 }
             ]
         },
+        {
+            "name" : "cmocka",
+            "buildsystem" : "cmake",
+            "builddir" : true,
+            "sources" : [
+                {
+                    "type" : "archive",
+                    "url" : "https://cmocka.org/files/1.1/cmocka-1.1.5.tar.xz",
+                    "sha256" : "f0ccd8242d55e2fd74b16ba518359151f6f8383ff8aef4976e48393f77bba8b6"
+                }
+            ]
+        },
         {
             "name" : "libphonenumber",
             "buildsystem" : "cmake-ninja",