wcc,ww: @test under separate compilation (M4 E1, #79)

Make `ww test --sep` work the Hare +test way: the -T synth test-main emits a
qualified test.run, and the test package is injected as an ordinary
separately-compiled dependency instead of splicing lib/test source into a
flat unit. Additive — combined stays the default and 910/997 are untouched
(their migration is M4 E2).

- compiler synth (both stages): the -T main emits N_DOT test.run plus a
  synthetic N_USE "test"; cmd/wcc/check.c + selfhost/cmd/wcc/check.ww.
- driver (both stages): build_one_sep gains is_test, injects the test package
  as a root dep, and passes -T to the root; do_test --sep routes a single-file
  test through the sep producer; cmd/ww/main.c + selfhost/cmd/ww/main.ww.
- 989_septest_run gate: ww test --sep on both stages, run-exit + cs==ww
  byte-id of the sep .s, non-vacuous.

The synth's test.run is left ty_err by the checker in both regimes (lib/test's
run is scope-keyed under "" not "test"; cgen emits the correct CALL via run's
//ww:module test directive) — wwstage tolerates it like cstage (rule-10). The
genuine fix, module-keying run under sep so the call type-resolves, is #80.

w6c_ww/wwdump_ww/ww_ww move (their embedded source changed); w6a_ww/w6l_ww and
the combined codegen output are unchanged.

cmd/wcc/check.c

@@ -3175,16 +3175,40 @@ check_file(Checker *c, Node *file)
 			scope_define_in_module(c->cur, tab->str, NULL, SK_VAR,
 			    tt, tab);
 
-			/* return run(__wwtests); */
+			/* return test.run(__wwtests);
+			 * QUALIFIED, not bare `run`: under the sep producer
+			 * lib/test is a real imported package, so the call must
+			 * carry the `test` module qualifier (N_DOT base ident
+			 * `test`, member `run`). The combined path tags the
+			 * auto-bundled lib/test `//ww:module test` too, so the
+			 * qualified form resolves+mangles identically there
+			 * (test.run either way) — byte-neutral. The base ident
+			 * resolves through a synthetic N_USE injected below. */
 			Node *arg = newnode(c->a, N_IDENT, fp);
 			arg->str = "__wwtests";
 			Node *call = newnode(c->a, N_CALL, fp);
-			call->lhs = newnode(c->a, N_IDENT, fp);
-			call->lhs->str = "run";
+			Node *dot = newnode(c->a, N_DOT, fp);
+			dot->lhs = newnode(c->a, N_IDENT, fp);
+			dot->lhs->str = "test";
+			dot->str = "run";
+			call->lhs = dot;
 			call->list = arg;
 			Node *ret = newnode(c->a, N_RETURN, fp);
 			ret->lhs = call;
 			body->list = ret;
+			/* synth `use test;` so the N_DOT base ident binds as a
+			 * module qualifier (SK_USE) and use_path maps `test` to
+			 * its import path. Mirror the typedecl-pass N_USE install
+			 * (check.c:2892). Appended to file->list below; emits no
+			 * asm (cgen keys off module-tagged decls). */
+			Node *usenode = newnode(c->a, N_USE, fp);
+			usenode->str = "test";
+			usenode->strlen = 4;
+			usenode->usepath = "test";
+			scope_define(c->cur, "test", SK_USE, NULL, usenode);
+			Node *ul = file->list;
+			if (ul == NULL) file->list = usenode;
+			else { while (ul->next) ul = ul->next; ul->next = usenode; }
 		}
 
 		Node *m = newnode(c->a, N_FNDECL, fp);