This patch modifies the include order to include headers from newlib
ahead of those from the core of Contiki. The only header file names
that are common between Contiki and newlib are assert.h and config.h,
but the config.h files in Contiki are only located in ports for other
CPUs so they are irrelevant to this patch. The motivation for this
patch is to cause files that include assert.h to include the one from
newlib that halts when an assertion fails. The assert implementation
in the core of Contiki does not halt when an assertion fails.
This patch also adds newlib syscall stubs that are required by the
newlib assert implementation and the _exit syscall function that halts
the system.
Finally, this patch updates some other newlib syscall stubs to
properly indicate their status as unsupported syscalls.
17b855aac9