w6c+selfhost: cross-module same-leaf type disambiguation via Sym.mod

test/wcc/data/modcollision/pos.ww

@@ -0,0 +1,18 @@
+// Positive case: two modules each export `type stream`. The consumer
+// imports both and disambiguates via the module qualifier. mod1.stream
+// has fields (a, b); mod2.stream has fields (c, d). The exit code
+// encodes a sum of all four fields, so any cross-binding would either
+// fail to compile or return the wrong value.
+
+use mod1;
+use mod2;
+
+fn main() i32 = {
+	let s1: mod1.stream;
+	s1.a = 3: i32;
+	s1.b = 5: i32;
+	let s2: mod2.stream;
+	s2.c = 7: i32;
+	s2.d = 11: i32;
+	return s1.a + s1.b + s2.c + s2.d;
+};