MFC r297790:
r297790 (by pfg):

libc: replace 0 with NULL for pointers.

While here also cleanup some surrounding code; particularly
drop some malloc() casts.

Found with devel/coccinelle.

MFC r292250:

Allow users override `DEBUG` on the command line via DEBUG_FLAGS="-DDEBUG" with
lib/libc/resolv by conditionalizing its definition

Reviewed by: ume, vangyzen
Differential Revision: https://reviews.freebsd.org/D4519

MFC r269867:
Update our stub resolver to final version of libbind
(libbind-6.0).

Obtained from: ISC

MFC r269867:
Update our stub resolver to final version of libbind
(libbind-6.0).

Obtained from: ISC