Makefile: link with -nostartfiles

This saves a bit more space and a reasonable thing to do since a
custom startup is used anyway.

Build-tested only.

Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Makefile: switch to newlib-nano

This makes the binary considerably smaller (73852 text with gcc
4.7.3, 71620 text with gcc 4.9.0 from TNT).

Build-tested only.

Signed-off-by: Paul Fertser <fercerpav@gmail.com>