Fix Ubuntu 18.04 Qt FTBFS (#1377)

* fix: avoid qt5_add_translation options on old qt5

Check the Qt5Linguist version before passing 'OPTIONS -silent' to
qt5_add_translation(). 'OPTIONS' arg support was merged 2018-01-12
https://codereview.qt.nokia.com/gitweb?p=qt%2Fqttools.git;a=commit;h=9f3dba2ea3978936565aa5e7893415a8a765268e
and made it into the 5.11 release on 2018-05-22.

* fix: ftbfs include <cassert> before using assert()

cmake/TrMacros.cmake

@@ -194,5 +194,9 @@ macro(tr_qt_add_resources)
 endmacro()
 
 macro(tr_qt_add_translation)
-    qt5_add_translation(${ARGN} OPTIONS -silent)
+    if (Qt5LinguistTools_VERSION VERSION_LESS 5.11.0)
+      qt5_add_translation(${ARGN})
+    else()
+      qt5_add_translation(${ARGN} OPTIONS -silent)
+    endif()
 endmacro()

qt/TorrentModel.cc

@@ -7,6 +7,7 @@
  */
 
 #include <algorithm>
+#include <cassert>
 #include <iostream>
 #include <utility>