Fix constant folding for shl/not

Since the source and destination types are the same the result should be
trimmed to fit.

tests/arithm/tnot.nim

@@ -0,0 +1,58 @@
+discard """
+  output: '''
+-5
+-5
+-5
+-5
+4
+4
+4
+4
+251
+65531
+4294967291
+18446744073709551611
+4
+4
+4
+4
+'''
+"""
+
+# Signed types
+block:
+  const t0: int8  = not 4
+  const t1: int16 = not 4
+  const t2: int32 = not 4
+  const t3: int64 = not 4
+  const t4: int8  = not -5
+  const t5: int16 = not -5
+  const t6: int32 = not -5
+  const t7: int64 = not -5
+  echo t0
+  echo t1
+  echo t2
+  echo t3
+  echo t4
+  echo t5
+  echo t6
+  echo t7
+
+# Unsigned types
+block:
+  const t0: uint8  = not 4'u8
+  const t1: uint16 = not 4'u16
+  const t2: uint32 = not 4'u32
+  const t3: uint64 = not 4'u64
+  const t4: uint8  = not 251'u8
+  const t5: uint16 = not 65531'u16
+  const t6: uint32 = not 4294967291'u32
+  const t7: uint64 = not 18446744073709551611'u64
+  echo t0
+  echo t1
+  echo t2
+  echo t3
+  echo t4
+  echo t5
+  echo t6
+  echo t7