base: make on mingw/cygwin

[Michael Scheibler]

When running make more than once following error occurs.

rm -f Headers/Foundation/*
mkdir Headers/Foundation
mkdir: cannot make directory `Headers/Foundation': File exists
make: [header-links] Error 1 (ignored)

That's because on mingw systems Foundation is created as a directory instead
of a symbolic link. Make should either use
rm -rf Headers/Foundation
or try to use symbolic links, as this is possible on cygwin's bash.




Michael