selfhost+cstage+test: graduate deflookup mod-qualified same-module-first (#11)

cstage Sdef walk #2 N_DOT branch used c->cur_mod where n->lhs->str is
the correct module hint. Sister of #4c wwstage graduation; same shape
as the TY_FN branch which already uses mafn(c, n->str, n->lhs->str).

cmd/w6c/cgen.c: add sdef_mod_match_hint(s, hint); walk #2 routes hint
first then head-pick fallback, matching #4a/#28/#31/#34 *mod variant
pattern. selfhost: add deflookuprhsmod(c, name, mod); cgdot N_DOT
mod-qualified str-def value-load routes through it. Rule-10 symmetric
stages: both stages now share the lhs.str polarity (was: both used
cur_mod / cur-module hint).

747_def_modqual_modshadow: table-driven sentinel — gamma calls
alpha.MSG with beta.MSG (same-leaf-name) at head of c.defs/sdefs.
want_imm "$38," (alpha strlit len), bad_imm "$27," (beta strlit len),
plus cs-vs-ws byte-id. Reverting cstage walk #2 to head-pick → fails
$38 on cstage + diverges cs-vs-ws; reverting wwstage cgdot to plain
deflookuprhs → fails $38 on wwstage.

make test 121/121; ww2==ww3==ww4 byte-id holds.

selfhost/cmd/wcc/cgen.ww

@@ -1730,6 +1730,29 @@ fn deflookuprhs(c: *cgen, name: str) *node = {
 	return nil;
 };
 
+// deflookuprhsmod — same-module-first walk for `mod.NAME` references.
+// Trio-leaf *mod variant mirroring fnretlookupmod (#31) / fnparamslookupmod
+// (#28) / enumlookupmod (#4a). Module-qualified `alpha.MSG` from a third
+// module needs the explicit alpha hint; deflookuprhs prefers c.curmod
+// (which doesn't match either source module on a 3rd-module qualifier)
+// and falls back to head-pick, possibly inlining beta.MSG's strlit when
+// both alpha and beta declare same-leaf str defs. cgdot's mod-qualified
+// str-def value-load routes here so a cross-module N_DOT collision
+// resolves to the explicit module. Falls back to deflookuprhs's bare-
+// leaf two-pass when no module matches.
+fn deflookuprhsmod(c: *cgen, name: str, mod: str) *node = {
+	if (mod.len > 0) {
+		let e: *defent = c.defs;
+		for (e != nil) {
+			if (streq(e.dname, name)) {
+				if (streq(e.dmod, mod)) { return e.drhs; };
+			};
+			e = e.dnext;
+		};
+	};
+	return deflookuprhs(c, name);
+};
+
 // ---- module-private symbol map --------------------------------------
 //
 // Every non-FFI top-level fn decl lives in its module's namespace —