cmake: Avoid using target_properties for old cmake

CMake versions less than 3.0 do not support the `target_sources`
command.  In order to be able to support v2.8.12.2 of cmake, directly
set the SOURCES property instead of using the target_sources command.

A future patch could reverse this, if the project decides to forgo
support for cmake versions less than 3.0.

Fixes #3801

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/programs/test/CMakeLists.txt b/programs/test/CMakeLists.txt
index 217741b..49b44e7 100644
--- a/programs/test/CMakeLists.txt
+++ b/programs/test/CMakeLists.txt
@@ -37,7 +37,8 @@
     endif()
 endforeach()
 
-target_sources(query_compile_time_config PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/query_config.c)
+set_property(TARGET query_compile_time_config APPEND PROPERTY SOURCES
+             ${CMAKE_CURRENT_SOURCE_DIR}/query_config.c)
 
 install(TARGETS ${executables_libs} ${executables_mbedcrypto}
         DESTINATION "bin"