Log Message:
Unbreak C++ on NetBSD, by popular demand.

Background:
LLVM 3.6 upstream added support for being a native toolchain on NetBSD.
This changed the default C++ runtime library from libstdc++ to libc++.
Patch this in pkgsrc's clang so we continue to use libstdc++ (for now)
Proper support for libc++ should be added later (perhaps w/ PKG_OPTIONs).
Thanks to Joerg for explaining the problem.