* src/Makefile.am (arch_sources): Add new file.
* src/estream.c (O_NONBLOCK): Move to 'gpgrt-int.h'.
(BUFFER_BLOCK_SIZE): Likewise.
(BUFFER_UNREAD_SIZE): Likewise.
(struct notify_list_s, notify_list_t): Likewise.
(struct _gpgrt_stream_internal, estream_internal_t): Likewise.
(X_POLLABLE): New macro.
(parse_mode): Parse keyword 'pollable', emulate O_NONBLOCK using the
same mechanism on Windows.
(_gpgrt_poll): Use the new '_gpgrt_w32_poll' on Windows.
* src/gpgrt-int.h (_gpgrt_functions_w32_pollable): New declaration.
(_gpgrt_w32_pollable_create): New prototype.
(_gpgrt_w32_poll): Likewise.
* src/w32-estream.c: New file.  This code is adapted from GPGME.
* tests/t-poll.c (create_pipe): Create pollable streams.