Merge pull request #1413 from Sarcasm/fix-openssl-test-compile-definitions

CMake: don't overwrite tls-test.c++ COMPILE_DEFINITIONS, append to it
diff --git a/c++/src/kj/CMakeLists.txt b/c++/src/kj/CMakeLists.txt
index 0a8614c..8788a20 100644
--- a/c++/src/kj/CMakeLists.txt
+++ b/c++/src/kj/CMakeLists.txt
@@ -271,9 +271,9 @@
     )
     target_link_libraries(kj-heavy-tests kj-http kj-gzip kj-tls kj-async kj-test kj)
     if (WITH_OPENSSL)
-      set_source_files_properties(compat/tls-test.c++
-        PROPERTIES
-          COMPILE_DEFINITIONS KJ_HAS_OPENSSL
+      set_property(
+        SOURCE compat/tls-test.c++
+        APPEND PROPERTY COMPILE_DEFINITIONS KJ_HAS_OPENSSL
       )
     endif()
     add_dependencies(check kj-heavy-tests)