[Qt][Win] Symbols are not exported in QtWebKit5.dll

[Qt][Win] Symbols are not exported in QtWebKit5.dll
https://bugs.webkit.org/show_bug.cgi?id=88873

Reviewed by Tor Arne Vestbø.

Source/WebKit:

* api.pri: Remove MAKEDLL setting done now in win32/default_post.prf.

Tools:

When linking the target dll make sure to re-export the symbols from
the static libraries marked as export, with the help of a little python
script and a qmake extra compiler.

* Scripts/generate-win32-export-forwards: Added.
* qmake/mkspecs/features/win32/default_post.prf:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@121261 268f45cc-cd09-0410-ab3c-d52691b4dbfc