improvements to get code size down for programs that don't use GC

tests/accept/run/tgenericassigntuples.nim

@@ -0,0 +1,16 @@
+discard """
+  output: '''abc232'''
+"""
+
+var t, s: tuple[x: string, c: int]
+
+proc ugh: seq[tuple[x: string, c: int]] = 
+  result = @[("abc", 232)]
+
+t = ugh()[0]
+s = t
+s = ugh()[0]
+
+echo s[0], t[1]
+
+