sim: nltvals: pull target errno out into a dedicated source file

sim: nltvals: pull target errno out into a dedicated source file

The current system maintains a list of target errno constants in the
nltvals.def file, then runs a build-time tool to turn that into a C
file.  This list of errno values is the same for all arches, so we
don't need the arch-specific flexibility.  Further, these are only
for newlib/libgloss environments, which makes it confusing to support
other userland runtimes (like Linux).  Let's simplify to make this
easier to understand & build.  We don't namespace the variables yet,
but sets up the framework for it.

Create a new target-newlib-errno.c template file.  The template file
is hand written, but the inline map is still automatically generated.

This allows us to move it to the common set of objects so it's only
built once in a multi-target build.

Now we can remove the output from the gentmap build-time tool since
it's checked into the tree.

Then we stop including the errno lists in nltvals.def since nothing
uses it.