talk-llama : fix build on macOS (#1062)
* talk-llama : use posix_madvise() instead of madvise() derived from BSD
sed -i 's,\<madvise\>,posix_&,g;s,\<MADV_,POSIX_&,g' examples/talk-llama/llama-util.h
* make : enable Darwin extensions for macOS builds
This is an attempt at fixing macOS build error coming from the fact that
RLIMIT_MEMLOCK define is not available there without Darwin extensions.
