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.

selfhost/test/sym_link.ww

@@ -0,0 +1,45 @@
+// selfhost/test/sym_link.ww — link-and-run probe for the ww-cgen
+// against the sym/typ/ast/mem dep stack. Exercises arena (mem),
+// hashtable scope (sym), and pulls in typ/ast as type carriers.
+// Returns 42 on success; smaller values name the probe that broke.
+
+use mem;
+use typ;
+use ast;
+use sym;
+
+export fn main() i32 = {
+	let a: *arena = newarena();
+	if (a == nil) { return 1; };
+
+	let s: *scope = newscope(a, nil);
+	if (s == nil) { return 2; };
+
+	let n1: str = "foo";
+	let r1: *sym = scope_define(s, n1, SK_VAR, nil, nil);
+	if (r1 == nil) { return 3; };
+
+	let n2: str = "bar";
+	let r2: *sym = scope_define(s, n2, SK_TYPE, nil, nil);
+	if (r2 == nil) { return 4; };
+
+	// Duplicate define in same scope must fail.
+	let r3: *sym = scope_define(s, n1, SK_VAR, nil, nil);
+	if (r3 != nil) { return 5; };
+
+	let l1: *sym = scope_lookup(s, n1);
+	if (l1 == nil) { return 6; };
+	if (l1.skind != SK_VAR) { return 7; };
+
+	let l2: *sym = scope_lookup(s, n2);
+	if (l2 == nil) { return 8; };
+	if (l2.skind != SK_TYPE) { return 9; };
+
+	// Not-found lookup returns nil.
+	let n3: str = "baz";
+	let l3: *sym = scope_lookup(s, n3);
+	if (l3 != nil) { return 10; };
+
+	freearena(a);
+	return 42;
+};