Fix walrus with member or index

[s-hadinger]

Fix a bug when using walrus operator with SETMEMBER or SETINDEX:

a = 1 import global def f() print(global.a := 42) end

When dumping f:

    ( &(const bvalue[ 2]) {     /* constants */
    /* K0   */  be_nested_str(global),
    /* K1   */  be_nested_str(a),
    }),
    &be_const_str_f,
    &be_const_str_solidified,
    ( &(const binstruction[ 6]) {  /* code */
      0x60000001,  //  0000  GETGBL	R0	G1
      0xB8060000,  //  0001  GETNGBL	R1	K0
      0x540A0029,  //  0002  LDINT	R2	42
      0x90060202,  //  0003  SETMBR	R1	K1	R2   <-- the result is in R2, and R1 contains `global`
      0x7C000200,  //  0004  CALL	R0	1
      0x80000000,  //  0005  RET	0
    })

With the fix, in such case an additional MOVE is added:

    ( &(const bvalue[ 2]) {     /* constants */
    /* K0   */  be_nested_str(global),
    /* K1   */  be_nested_str(a),
    }),
    &be_const_str_f,
    &be_const_str_solidified,
    ( &(const binstruction[ 7]) {  /* code */
      0x60000001,  //  0000  GETGBL	R0	G1
      0xB8060000,  //  0001  GETNGBL	R1	K0
      0x540A0029,  //  0002  LDINT	R2	42
      0x90060202,  //  0003  SETMBR	R1	K1	R2
      0x5C040400,  //  0004  MOVE	R1	R2      <-- this brings back the result in R1
      0x7C000200,  //  0005  CALL	R0	1
      0x80000000,  //  0006  RET	0
    })

[s-hadinger]

@skiars would you be kind enough to approve all the open PRs, I can't merge them otherwise

[skiars]

I'm looking at these PRs.

[s-hadinger]

Fixing a regression bug (found by sfromis):

class confused_walrus
  var b
  def f()
    var c = 1
    if self.b := true
      c = 2
    end
    return self
  end
end
print(confused_walrus().f())
# prints 'true' instead of the instance

Now fixed with latest commit.