SET(LIBRARY_OUTPUT_PATH ${CMAKE_CURRENT_BINARY_DIR}/bin)
SET(EXECUTABLE_OUTPUT_PATH ${CMAKE_CURRENT_BINARY_DIR}/bin)

IF(CMAKE_CONFIGURATION_TYPES)
  SET(sub_CONFIG_TYPE -C "${CMAKE_CFG_INTDIR}")
ELSE(CMAKE_CONFIGURATION_TYPES)
  SET(sub_CONFIG_TYPE)
ENDIF(CMAKE_CONFIGURATION_TYPES)

ADD_CUSTOM_COMMAND(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/sub-fake
                   COMMAND ${CMAKE_CTEST_COMMAND}
                   ARGS ${sub_CONFIG_TYPE}
                        --build-and-test
                        ${CMAKE_CURRENT_SOURCE_DIR}/sub   # dir containing CMakeLists.txt file
                                                          # which could probably do
                                                          # a glob to find sources
                        ${CMAKE_CURRENT_BINARY_DIR}/sub-build   # where to build it
                        --build-noclean
                        --build-two-config
                        --build-project sub  # name of library from sub/CMakeLists.txt 
                        --build-generator ${CMAKE_GENERATOR}
                        --build-makeprogram ${CMAKE_MAKE_PROGRAM}
                        --build-options 
                             # put compiled library where we want it
                             -DLIBRARY_OUTPUT_PATH:PATH=${LIBRARY_OUTPUT_PATH}
                        # can/should add other options such as compilers,
                        # build type, compile flags, etc ...
                        )
ADD_CUSTOM_TARGET(sub-target ALL DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/sub-fake)

INCLUDE_DIRECTORIES(sub)
ADD_EXECUTABLE(main main.cpp)
TARGET_LINK_LIBRARIES(main ${LIBRARY_OUTPUT_PATH}/libsub.a)  # full path for dependencies
ADD_DEPENDENCIES(main sub-target)   # make sure sub is built before building executable