Fix `DEBUG_POSTFIX` property (#746)

The generator expressions here are actually unnecessary, now that I think about it.

This should fix #745

CMakeLists.txt

@@ -117,7 +117,7 @@ set_target_properties(yaml-cpp PROPERTIES
   VERSION "${PROJECT_VERSION}"
   SOVERSION "${PROJECT_VERSION_MAJOR}.${PROJECT_VERSION_MINOR}"
   PROJECT_LABEL "yaml-cpp $<IF:${build-shared},shared,static>"
-  DEBUG_POSTFIX $<$<AND:$<NOT:${build-shared}>,$<CONFIG:Debug>>:d>)
+  DEBUG_POSTFIX d)
 
 configure_package_config_file(
   "${PROJECT_SOURCE_DIR}/yaml-cpp-config.cmake.in"