Fix passing from command line

Author: TsynkPavel

CMakeLists.txt

@@ -101,7 +101,9 @@ set(CMAKE_LIBRARY_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/lib" CACHE PATH "Library
 set(CMAKE_PDB_OUTPUT_DIRECTORY     "${CMAKE_BINARY_DIR}/bin" CACHE PATH "PDB (MSVC debug symbol)output dir.")
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/bin" CACHE PATH "Executable/dll output dir.")
 
-set(JSONCPP_USE_SECURE_MEMORY "0" CACHE STRING "-D...=1 to use memory-wiping allocator for STL")
+if(JSONCPP_USE_SECURE_MEMORY)
+    add_definitions("-DJSONCPP_USE_SECURE_MEMORY=1")
+endif()
 
 configure_file("${PROJECT_SOURCE_DIR}/version.in"
     "${PROJECT_BINARY_DIR}/version"