Let DEBUG be overridden on the command line with lib/libc/resolv
I ran into compilation issues when trying to do make DEBUG_FLAGS="-g -O0 -DDEBUG"
with libc because the definitions mismatched (nothing vs #defined as 1).
This fixes the issues in lib/libc/resolv with duplicate definitions
MFC after: 1 week
Sponsored by: EMC / Isilon Storage Division