CMAKE in VS 2019 16.11.1 warns about missing file extensions for XML-related tests: (#69)

diff --git a/src/test/cpp/xml/CMakeLists.txt b/src/test/cpp/xml/CMakeLists.txt
index 138c489..cd54de6 100644
--- a/src/test/cpp/xml/CMakeLists.txt
+++ b/src/test/cpp/xml/CMakeLists.txt
@@ -1,7 +1,7 @@
 add_executable(xmltests
-    domtestcase
-    xmllayouttest
-    xmllayouttestcase
+    domtestcase.cpp
+    xmllayouttest.cpp
+    xmllayouttestcase.cpp
 )
 
 target_link_libraries(xmltests PRIVATE ${APR_UTIL_LIBRARIES} EXPAT::EXPAT)