ch15/15.9/15.9.5/15.9.5.43/15.9.5.43-0-8 fails when US enters summer time

The ch15/15.9/15.9.5/15.9.5.43/15.9.5.43-0-8 test from the ES5 tests began failing on March 11th when the US time zones enter summer time daylight savings.

Reduced test-case (can be reduced further of course):

function runTestCase(testcase) {
    if (testcase() !== true) {
        print("Test case returned non-true value!");
    }
}

function testcase() {
        var timeZoneMinutes = new Date().getTimezoneOffset() * (-1);
        var date, dateStr;
        try {
            if (timeZoneMinutes > 0) {
                date = new Date(1970, 0, -99999999, 0, 0, 0, -1);
            } else {
                date = new Date(1970, 0, -99999999, 0, 0 + timeZoneMinutes - 60, 0, -1);
            }

            dateStr = date.toISOString();

            return false;
        } catch (e) {
            return e instanceof RangeError;
        }
    }
runTestCase(testcase);

Run with qmljs test.js and observe how with TZ="America/Vancouver" qmljs test.js it fails (on Linux box configured to CET).

When "passes" we run into the first if() and the resulting date object is a NaN because the intermediate double value crosses the 8.64e15 threshold in TimeClip, causing the toISOString() call to throw the expected range error.

When it "fails" we have timeZoneMinutes == -420 and end up with -480 as value for the minutes parameter to the Date constructor. The resulting intermediate double value passed to TimeClip is just below the 8.64e15 threshold and we don't generate a NaN date.