They can't "make clang proprietary". they can take the code, re-license and start a privative fork off that ... but in that case the code of clang would still be open and the community can keep the work with it.Say Apple for some reason makes clang proprietary, can the open source community not fork and continue to develop the last open source version of clang before it became proprietary?
GPL doesn't give any *absoluto* warranty about privative abuse (as some people want you to think), we had PLENTY of examples of that even in the kernel itself (if we put it that way). so this is nonsense, lot's of BSD-licensed projects may be forked or re-used partially, but the original project is still open ... so no, it doesn't threaten in any way the FOSS community. but as I said in the previous thread: licensing is a hard topic, the BSD is a license that is hard to pick where to use. in some cases it's a better choice than GPL, sometimes it's the other way.
It's not a black or white thing, it's a topic with much more colors.
P.S → Here's an article I cited in the previous thread that I would like to link again : http://www.theregister.co.uk/2011/05...rs_and_takers/