[LyX/master] Fix linking errors for check_filetools, check_trivstring, check_convert, check_lstrings

[Kornel Benko]

commit 35eabe1ea7c942503e3f65f3bbb6b89a965216c4
Author: Kornel Benko <kor...@lyx.org>
Date:   Fri Dec 22 07:19:13 2017 +0100

    Fix linking errors for check_filetools, check_trivstring, check_convert, 
check_lstrings
    
    This may amend f1df7e478da5934a77436f039429d8d2411f3efb
---
 src/support/tests/dummy_functions.cpp |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/src/support/tests/dummy_functions.cpp 
b/src/support/tests/dummy_functions.cpp
index b7dcf6f..773a426 100644
--- a/src/support/tests/dummy_functions.cpp
+++ b/src/support/tests/dummy_functions.cpp
@@ -61,4 +61,12 @@ namespace lyx {
                static frontend::FontMetrics dummy;
                return dummy;
        }
+
+       struct App {
+               bool cancel_export;
+       };
+
+       App app;
+       App theApp() { return app; }
+
 } // namespace lyx