Initial port of libcxx to Unikraft

This is our initial port of libcxx to Unikraft as an external
library. Libc is requiered for it to work. The dependency list
should contain: ...:$(UK_LIBS)/libunwind:
$(UK_LIBS)/compiler-rt:$(UK_LIBS)/libcxxabi:$(UK_LIBS)/libcxx:
$(UK_LIBS)/newlib:...

Signed-off-by: Vlad-Andrei Badoiu <vlad_andrei.badoiu@stud.acs.upb.ro>
Reviewed-by: Felipe Huici <felipe.huici@neclab.eu>

Add .gitignore

Signed-off-by: Vlad-Andrei Badoiu <vlad_andrei.badoiu@stud.acs.upb.ro>
Reviewed-by: Felipe Huici <felipe.huici@neclab.eu>

Initial commit (empty)