User-defined function calls are rejected in expression position

[michaelsutton]

Internal function calls currently work in assignment form, but fail when used directly inside an expression.

This compiles:

contract Calls() {
    function one() : (int) {
        return(1);
    }

    entrypoint function main() {
        (int value) = one();
        require(value == 1);
    }
}

but this fails:

contract Calls() {
    function one() : (int) {
        return(1);
    }

    entrypoint function main() {
        require(one() == 1);
    }
}

with:

unknown function call: one

This looks like statement-level calls are handled by inline expansion, while expression-position calls go through the builtin-only function-call path and never resolve user-defined functions.