Make errno a thread-local variable.

errno is supposed to be thread local and we do that here in a rather
makeshift way by implementing a function that returns a pointer to
the __errno variable in the thread block.

If more serious TLS is required, perhaps it would be worthwhile
implementing it using the linker and the "__thread" storage attribute.
That's a bit overkill just for this. I'm also not liking what I saw
the compiler producing.

Change-Id: I03bc0bd6a89f6e3d6bae7653284ee01054614f9a
Reviewed-on: http://gerrit.rockbox.org/803
Reviewed-by: Michael Sevakis <jethead71@rockbox.org>
Tested: Michael Sevakis <jethead71@rockbox.org>
5 files changed