Install the compatibility symlink to libpython.a on OSX using 'ln -sf' instead

of 'ln -s', this avoid problems when reinstalling python.

Makefile.pre.in

@@ -935,7 +935,7 @@ frameworkinstallstructure:	$(LDLIBRARY)
 # Install a number of symlinks to keep software that expects a normal unix
 # install (which includes python-config) happy.
 frameworkinstallmaclib:
-	ln -s "../../../Python" "$(DESTDIR)$(prefix)/lib/python$(VERSION)/config/libpython$(VERSION).a"
+	ln -fs "../../../Python" "$(DESTDIR)$(prefix)/lib/python$(VERSION)/config/libpython$(VERSION).a"
 	cd Mac && $(MAKE) installmacsubtree DESTDIR="$(DESTDIR)"
 
 # This installs the IDE, the Launcher and other apps into /Applications