Reduce the command line length when generating bindings

With a working directory of only a few characters longer than our
build machines it's easy to end up getting a
"NMAKE : fatal error U1095" on Windows.

Unlike when invoking the compiler or the linker, we do not use
response files to pass to perl when generating JavaScript bindings.

Reduce the likeliness of getting this error for people building
QtWebKit themselves by avoiding specifying disabled features.
The binding generators do not include Platform.h like the normal
code does.

Task-Number: QTBUG-38632
Change-Id: Iaa1a1c75e8f6a6391f896067adbc5f3b55b59007
Reviewed-by: Michael Bruning <michael.bruning@digia.com>