Add threadpool-legacy.c to Makefile

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

Initial port of pthreadpool to Unikraft

This is our initial port of pthreadpool to Unikraft as an external library. Libfxdiv
and pthreads are required. When adding the library to the dependency list, this
library should come after libfxdiv.
(e.g. ...:$(UK_LIBS)/libunwind:$(UK_LIBS)/compiler-rt:$(UK_LIBS)/libcxxabi:
$(UK_LIBS)/libcxx:$(UK_LIBS)/pthread-embedded:$(UK_LIBS)/newlib:
$(UK_LIBS)/fxdiv:(UK_LIBS)/pthreadpool:...)

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

Add documentation

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)