bugfix: generic instantiation across module boundaries

tests/accept/run/ttables.nim

@@ -0,0 +1,18 @@
+discard """
+  output: '''true'''
+"""
+
+import hashes, tables
+
+var t = initTable[tuple[x, y: int], string]()
+t[(0,0)] = "00"
+t[(1,0)] = "10"
+t[(0,1)] = "01"
+t[(1,1)] = "11"
+
+for x in 0..1:
+  for y in 0..1:
+    assert t[(x,y)] == $x & $y
+
+echo "true"
+