webkit: fix build with bison 2.6

webkit: fix build with bison 2.6

WebKit 1.2.7 does not build with Bison 2.6, but Bison 2.6 is our
host-bison, so if the build machine has bison 2.6, or if by chance it
gets built before webkit, then the build fails with errors such as:

  http://autobuild.buildroot.org/results/0b7cfbebd4388cabfa243b5ef74e3b6316fd9fd9/build-end.log

(the real error is not visible due to the overwhelming number of
warnings).

So, we add a patch that modifies WebKit to make it compatible with
Bison 2.6 (patch taken from upstream), and we also add 'host-bison' to
the WebKit dependencies, so that we are sure that a well-known version
of bison is used.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>