Thanks for your reply. The include does not change the issue. It is not surprising because I had added the library with its absolute path so there was no ambiguity there/
Also the error message refers to the absolute path of the library file.
I was reading about GCC and came accross a comment that in the Unix world GCCs add the prefix and the suffix automatically to the library name that is give with the -l option, Could it be the problem ? Would be strange that the Eclipse interface does not take that into account.
I found a work around:
Create the libXXXX.a archive as initially described.
Copy it in the folder : iotdk-ide-win\devkit-x86\sysroots\i586-poky-linux\usr\lib
In the project using the lib : Add the lib XXXX to the list in Properties>C/C++ General>Paths and Symbols>Libraries (! not libXXXX.a but just XXXX)
.. then all works out nicely