Resolve QtScript's patches to JavaScriptCore

The QtScript that ships with Qt since 4.6 uses a forked JavaScriptCore (src/3rdparty/javascriptcore). The patches can be divided into two categories:

• Compile fixes for Qt tier 2 platforms. These are tracked upstream at https://bugs.webkit.org/show_bug.cgi?id=36493
• Patches that help maintain functional and behavioral compatibility with the old (pre-4.6) QtScript back-end. (Because of the source+binary policy of Qt, we can't change or drop any of the API until Qt 5, and we need to be very careful with behavorial changes.)

For each patch, there are four possible resolutions:

• Upstream the patch to WebKit.
• Change the QtScript implementation so that the patch is no longer needed (possibly at e.g. performance cost).
• Drop the patch, causing a behavorial change.
• Keep the patch (meaning that the fork can never be dropped completely).

Relevant aspects to consider for each patch:

• Which Qt tests break if the patch is not applied?
• Is the patch ECMA compliance-related, or a "quirk" of the old QtScript implementation, or something else?
• What's the perceived impact of dropping the patch?
• Can functionality be deprecated (but hopefully still work) in favor of new API that doesn't require JSC patches?