cygwin build on appveyor fails attempting to use linux calls?

[James E. King, III]

While attempting to build Boost.Random on Appveyor using a cygwin job, this happens:

​https://ci.appveyor.com/project/jeking3/random/build/1.0.10-develop/job/h9m6ca7nho5hd7w7

The pull request is: ​https://github.com/jeking3/random/pull/1

The error is:

In file included from libs\test\src\debug.cpp:16:0:
./boost/test/impl/debug.ipp: In function 'const char* boost::debug::{anonymous}::prepare_gdb_cmnd_file(const boost::debug::dbg_startup_info&)':
./boost/test/impl/debug.ipp:424:23: error: '::mkstemp' has not been declared
     fd_holder cmd_fd( ::mkstemp( cmd_file_name ) );
                       ^
In file included from libs\test\src\debug.cpp:16:0:
./boost/test/impl/debug.ipp: In function 'bool boost::debug::attach_debugger(bool)':
./boost/test/impl/debug.ipp:892:34: error: '::mkstemp' has not been declared
     fd_holder init_done_lock_fd( ::mkstemp( init_done_lock_fn ) );
                                  ^
./boost/test/impl/debug.ipp:929:9: error: '::select' has not been declared
         ::select( 0, 0, 0, 0, &to );