Fix "make lcov" in CMake out-of-tree builds

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index bc02627..ca477ac 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -97,6 +97,7 @@
     if(EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/seedfile")
         link_to_source(seedfile)
     endif()
+    link_to_source(Descriptions.txt)
     link_to_source(compat.sh)
     link_to_source(context-info.sh)
     link_to_source(data_files)