Automaticaly create needed folder when building

[uNouss]

#35 Need to be fixed before this issue to not be bothered by this one.

To reproduce:

• clone the project
• jump into to syntax/trunk folder
• issue the following command to build sh etc/bin/sxmake

At this point, some folders may be missing, and the build will stop without explicitly saying that the required folder is missing (for example, as shown below, the lib folder in ./bnf folder).

_.log:error: unable to open output file '.../syntax/trunk/bnf/lib/bnf_folcon.o': 'No such file or directory'

And this happens for several other {bnf,csynt,lecl,paradis,prio,recor,semact,semat,semc,tables,tdef}/lib folders.

Expected behaviour is to automaticaly create these folders supfolder/lib.

The same happens with sh etc/bin/sxmake j77. There are missing folders, for examples: examples/{j77,f77,..}/lib