Initial build warns about removing non-existing library

[sperretta]

When first running make, the lib/*.a targets complain about not being able to remove the static libraries, for example:

rm: cannot remove 'lib/mylib.a': No such file or directory

This could be suppressed by passing -f to rm.

[m8pple]

Thanks, I hadn't noticed that on fresh clones and checkouts.

I'll modify as suggested.