Patch safe-ctype.h for new libc++ (patch from: FreeBSD Ports, r325805)
Patch script.cc to work around clang bug #7927
Patch system.h for new libc++ (ported gold.h patch from: FreeBSD Ports, r325806)
- clang-specific code to check whether __has_include(<unordered_set>)
- CXX11-specific definitions for unordered set,map and multimap