Always do 'setup makefile' before building each library

This forces preprocessing to happen, which is necessary if any of the
.hsc files have been modified.  Without this change, a 'setup
makefile' would be required by hand after a .hsc file changed.
Fortunately 'setup makefile' isn't much extra work, and I've made it
not overwrite GNUmakefile if it hasn't changed, which avoids
recalculating the dependencies each time.