Expressions for const definitions in FunC allow defining variables

[akifoq]

The following code

const int x = (int y = 2) + 2;

_ main() {
  return y;
} 

causes the FunC compiler to crash

// automatically generated from `1.fc` 
DECLPROC main
main PROC:<{
fatal: Assertion failed at /usr/src/ton/crypto/func/func.h:1621: i >= 0 && i < depth() && "invalid stack reference"

FunC version: 0.4.4