Fix debug build on Windows.

Checking for WITH_DEBUG does not work, as described in CMake MySQL wiki
http://forge.mysql.com/wiki/CMake#Debug-only_options

Excluding  directory completely for certain build types works for Makefiles only,  but not for Visual Studio and not for Xcode.

CMakeLists.txt

@@ -285,10 +285,12 @@ SET (MYSQLD_STATIC_PLUGIN_LIBS "" CACHE INTERNAL "")
 ENDIF()
 
 ADD_SUBDIRECTORY(include)
-IF(WITH_DEBUG)
-  ADD_SUBDIRECTORY(dbug)
+IF(CMAKE_GENERATOR MATCHES "Makefiles" AND NOT CMAKE_BUILD_TYPE MATCHES "Debug")
+  SET(DBUG_LIBRARY)
+ELSE()
   SET(DBUG_LIBRARY dbug)
-ENDIF(WITH_DEBUG)
+  ADD_SUBDIRECTORY(dbug)
+ENDIF()
 ADD_SUBDIRECTORY(strings)
 ADD_SUBDIRECTORY(vio)
 ADD_SUBDIRECTORY(regex)