An application might want to use C11 features. The user would assume
that setting `CFLAGS=-std=gnu11` in the Makefile would work. It does not
since the board's Makefile.include shadows the `-std` flag.
This patch removes the `-std=gnu99` from the various Makefile.includes,
and sets the flag in the common Makefile.include of RIOT instead.
If an `-std` flag was provided by an earlier Makefile (the application,
the board, or the CPU [whilst only the former one should]), then no
additional flag is set. It is first tested if the supplied compiler
understands `-std=gnu99`, then `-std=c99`.
* add missing $(AD) to osx $(LINK) invocation
* move osx build determination to native makefile
* move old libc test to native makefile
* set objcopy to "true" - it is superfluous for native no matter what the system is
* add some documentation to natives makefile
wrap some libc functions that do system calls (terminal output)
wrap read/write with syscall guard
define real_read/write (next dynamic linker find for read/write)
guard system calls in remaining code
introduce native_internhal.h
throw out some debug statements that break things
clean up includes a bit
declare board_init in native_internhal.h
add -ldl to LINKFLAGS for cpu/syscalls
