[CMake] eclipse possible bug

[Andrea Galeazzi]

suppose I have a project with:
add_subdirectory("path/lib1"  "${CMAKE_CURRENT_BINARY_DIR}/ib1")
when I change a source of lib1 and click on build over the eclipse 
project, eclipse doesn't build anything.
If I change a source of the main project it launches the build correctly.
I also tried to test the same thing with a simple MinGW Makefile 
(instead of Eclipse CDT 4 - MinGW Makefile) and it works properly in 
both two cases.