The file list of c-ares 1.15.0 is used for 1.16.1 since the following files are
the same:
1. modules/c-ares/1.16.1/patches/add_build_file.patch
2. modules/c-ares/1.15.0/patches/add_build_file.patch

And add_build_file.patch is adapted from
https://github.com/grpc/grpc/tree/master/third_party/cares. I have tried to find
c-ares version 1.16.1 in grpc project. A search of grpc project commit log shows
that the most relevant thing is commit bdb3f860649bb4c136ba36bad3d9363fccbd29fa
which mentions '-DgRPC_CARES_PROVIDER=package with c-ares 1.16.0 overrides'. My
guess is that grpc has upgraded c-ares from 1.15.0 to 1.17.2 directly.

I built c-ares 1.16.1 with `buildconf` on macOS. The resulted Makefile has
the following two file list:
1. CSOURCES: C++ source files.
2. HHEADERS: C++ header files.

A comparison of CSOURCES with cc_library srcs attribute shows that some source
files are missing. ares_getopt.c is unneeded ares_getopt is not include in
CSOURCES. It is included in SAMPLESOURCES. So this commit deletes it. This
commit also adds the missing C++ source files.

A comparison of HHEADERS with cc_library hdrs attribute shows that hdrs has
three extra files:
1. ares_config.h
2. config-win32.h
3. ares_getopt.h

ares_getopt.h will be deleted together with ares_getopt.c. Since I am not sure of
the reason why the other two files exist, they are kept untouched.

Fix #77

update

update