Nettool makefile for MingW needs wsock32.
ifeq ($(OSTYPE),mingw)
CC ?= gcc
OS_OPT ?= -mno-cygwin -march=pentium
# we need the libraries EXACTLY in this order to link
STD_LIBS = -lmingw32 -lstdc++ -lwsock32
endif
And this is not an error, but curses doesn't need for MingW.
g++.exe: -lcurses: linker input file unused because linking not done
===> LD ../build/default/nettool/nettool