Birdtest: Purge 'int main()' from lib/birdlib.a #2

Birdtest: Purge 'int main()' from lib/birdlib.a #2

All origin static functions from sysdep/unix/main.c were rewrited to
non-static.

All origin static global variables from sysdep/unix/main.c was rewrited
to extern.

It is possible create executables bird, birdc and birdcl as well as run
unit tests without mockuping

After remake new BIRD's build system will be this commit reverting...