tclibc-newlib: Adds a new TCLIBC variant to build with newlib as C library
This patch adds the posibility to build using TCLIBC=newlib.
It allows users to build baremetal applications with the use of a
C library.
Newlib is a lightweight C library meant to be used on embedded systems,
it is meant to be easily portable for new platforms and to provide
basic functionality on them, by design, it provides stubs for some of
these core functions declared as weak, so they can be built correctly
and then linked against some other library which provides specifics
about the platform being used if need be, libgloss takes care of these
in some cases, but it can also be extended, this patch also allows the
user to easily add other libraries to it by adding them to
NEWLIB_EXTENDED for this specific reason.
