Darwin: posix threads, copy sdk option

Set CT_THREADS="posix" in sample configs.
Add --with-gxx-include-dir=/usr/include/c++/4.2.1 to
 gcc and llvmgcc configure.
Add 'Copy SDK to sysroot' option to DARWIN.
Update Apple sample configs so that 10 copies the SDK
 to the sysroot and 11 does not.