Invalid emitted code for await expression

[yortus]

TypeScript Version: 2.1.0-dev.20160821

Code

// Just for reference... the error here is correct and expected
function* foo() {
    !yield 42; // ERROR: Expression expected
}

// This one emits bad code...
async function bar() {
    !await 42; // OK
}

// ----------
// generated .js code for the bar function:
function bar() {
    return __awaiter(this, void 0, void 0, function* () {
        !yield 42;                                           // <===== (1) bad emit here
    });
}

Expected behavior:
The emitted code is valid.

Actual behavior:
The emitted code is invalid at (1). !yield 42 is not a valid expression as demonstrated in the foo function. Also the generated code fails at runtime at (1) in both V8 and Edge.

[yortus]

I think this might have been surfaced by #9890? A few days ago in 2.1.0-dev.20160818, the !await 42 expression would not compile anyway, so the emitted code didn't matter, but now I guess it does.