ww: import toolchain — C bootstrap + ww-side self-host (phases 0-10)

C bootstrap (phases 0-9):
  cmd/wwc, cmd/6c, cmd/6a, cmd/6l, cmd/ww, rt, lib/*.

ww-side self-host (phase 10):
  selfhost/cmd/wwc — ww-cgen frontend; bootstrap fixed point.
  selfhost/cmd/6a  — assembler; byte-identical to C 6a (test 991).
  selfhost/cmd/6l  — linker w/ archive (.a) support; byte-identical
                     to C 6l (test 992).
  selfhost/cmd/ww  — driver (build/run/version); byte-identical to
                     C ww (test 993).

make test: 15/15. make bootstrap: ww2.s == ww3.s, ww2.o == ww3.o,
ww2 == ww3 byte-identical, with the full ww-tooled chain.

lib/io/stream.ww

@@ -0,0 +1,28 @@
+// io — stream interface (Plan 9 Bio / Hare io::stream shape).
+//
+// No closures, no methods. A `stream` is a struct of function
+// pointers plus a `ctx: *void`. The error channel is the return
+// value of read/write/close. Negative i32 = errno-style code,
+// non-negative = bytes transferred.
+
+type stream = struct {
+	ctx:    *void,
+	read:   fn(s: *stream, buf: []u8) i32,
+	write:  fn(s: *stream, buf: []u8) i32,
+	close:  fn(s: *stream) i32,
+};
+
+def eof:    i32 = -1;
+def closed: i32 = -2;
+
+export fn stream_read(s: *stream, buf: []u8) i32 = {
+	return s.read(s, buf);
+};
+
+export fn stream_write(s: *stream, buf: []u8) i32 = {
+	return s.write(s, buf);
+};
+
+export fn stream_close(s: *stream) i32 = {
+	return s.close(s);
+};