io_win32_unittest: make //:win32_test run again
io_win32_unittest: make //:win32_test run again

Do not use "googletest.h", apprently that leads to
linking errors on Windows which I couldn't figure
out how to solve, and decided to just go with
plain gTest instead.

See https://github.com/google/protobuf/issues/3951

google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf