Wasm_x86: support functions return value

[ubaidsk]

This PR adds support for return values of function calls.

Example:

def A_Sqr(x: i32) -> i32:
    return x * x

def ComputeCircleArea(radius: i32) -> i32:
    pi: i32
    pi = 3
    return pi * A_Sqr(radius)

def Main0():
    print(ComputeCircleArea(5))

Main0()

Output:

(lp) ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/OpenSource/lpython$ lpython examples/expr2.py --backend x86
(lp) ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/OpenSource/lpython$ ./a.out 
75
(lp) ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/OpenSource/lpython$ lpython examples/expr2.py --backend wasm_x86
(lp) ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/OpenSource/lpython$ ./a.out 
75(lp) ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/OpenSource/lpython$ 

Only the latest/recent two commits are part of this PR. The rest of the commits are part of #1223. I will rebase this PR once #1223 is merged.

[ubaidsk]

In the above example, the function Sqr() is named as A_Sqr() so that it gets defined before the function ComputeCircleArea() which calls it.

[ubaidsk]

Another example, with (unnecessary) local variables inside A_Sqr(). The unnecessary local variables testify that the return value is being properly/appropriately handled.

def A_Sqr(x: i32) -> i32:
    y: i32
    z: i32
    y = 2
    z = 5
    x = y + z
    return x * x

def ComputeCircleArea(radius: i32) -> i32:
    pi: i32
    pi = 3
    return pi * A_Sqr(radius)

def Main0():
    print(ComputeCircleArea(5))

Main0()

Output:

(lp) ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/OpenSource/lpython$ lpython examples/expr2.py --backend x86
(lp) ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/OpenSource/lpython$ ./a.out 
147
(lp) ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/OpenSource/lpython$ lpython examples/expr2.py --backend wasm_x86
(lp) ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/OpenSource/lpython$ ./a.out 
147(lp) ubaid@ubaid-Lenovo-ideapad-330-15ARR:~/OpenSource/lpython$ 

[ubaidsk]

This is ready. Please possibly review and please share feedback.

[ubaidsk]

It seems, we can combine the X86Generator and X86Visitor classes. I created a demo PR for the same here ubaidsk#1. Please possibly review and share if we shall combine the two classes.

[ubaidsk]

It seems, we can combine the X86Generator and X86Visitor classes. I created a demo PR for the same here ubaidsk#1. Please possibly review and share if we shall combine the two classes.

I submitted the above change as a regular PR at #1257.