Scope checking issue with unverified build of pancake

[KurtWu10]

The current master branch of unverified pancake compiler (commit: 4e312c0, HOL: e6d0417) fails to compile the following simple program

fun main() {
  return 0;
}

To reproduce, compile cake in unverified/sexpr-bootstrap/x64/64, and then compile the program with cake --pancake. It returns

### ERROR: scope error
AT (2:9 2:10): function main is not in scope in function main

Program exited with nonzero exit code.

The verified build (compiler/bootstrap/compilation/x64/64) works fine.