generated when necessary libraries are not found

All projects output directories are now common in
the top level. This commit takes care of the
CMAKE_CONFIGURATION_TYPES for Visual Studio.

With this commit the Find_XXX.cmake files do not need
HINTS anymore since all targets are built in a same
directory known to CMAKE_LIBRARY_PATH, and all headers
directories are referenced in CMAKE_INCLUDE_PATH.

Had to pass g3log_SOURCE_DIR from the superbuild to
the inner build to be able to find the librairies for
g3log in Findg3log.cmake.