Merge: Memcpy -> memmove

As discussed in #655, this PR replaces the uses of memcpy in standard by memmove, a safer alternative while not costing that much more.

Before : 0m15.584s
After : 0m15.748s

Pull-Request: #661
Reviewed-by: Jean Privat <jean@pryen.org>

diff --cc src/abstract_compiler.nit
Simple merge

diff --cc src/global_compiler.nit
Simple merge

diff --cc src/separate_compiler.nit
Simple merge