Use malloc_trim only on linux

This is not the correct fix but a temporary one, this allow us
to compile on freebsd while a better fix is in the works.

src/Screen.cpp

@@ -1703,10 +1703,12 @@ void Screen::setScroll(const HistoryType &t, bool copyPreviousScroll)
         t.scroll(_history);
     }
 
+#ifdef Q_OS_LINUX
 #ifdef __GNUC__
     // We might have been using gigabytes of memory, so make sure it is actually released
     malloc_trim(0);
 #endif
+#endif
 }
 
 bool Screen::hasScroll() const