Patch taken from Nix:
   https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/libraries/qt-5/5.11/qtwebkit.patch

diff --git a/Source/WebKit2/PlatformQt.cmake b/Source/WebKit2/PlatformQt.cmake
--- a/Source/WebKit2/PlatformQt.cmake
+++ b/Source/WebKit2/PlatformQt.cmake
@@ -261,6 +261,7 @@
 list(APPEND WebKit2_SYSTEM_INCLUDE_DIRECTORIES
     ${GLIB_INCLUDE_DIRS}
     ${GSTREAMER_INCLUDE_DIRS}
+    ${GSTREAMER_PBUTILS_INCLUDE_DIRS}
     ${Qt5Quick_INCLUDE_DIRS}
     ${Qt5Quick_PRIVATE_INCLUDE_DIRS}
     ${SQLITE_INCLUDE_DIR}

/'>index</a> : <a href='/guix/'>guix</a></td><td class='form'><form method='get'>
<input type='hidden' name='id' value='41f058d10d17802632a1354eb02dd363057ded4b'/><input type='hidden' name='showmsg' value='1'/><select name='h' onchange='this.form.submit();'>
<option value='koszko' selected='selected'>koszko</option>
<option value='koszko-scripts'>koszko-scripts</option>
</select> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=41f058d10d17802632a1354eb02dd363057ded4b'>refs</a><a class='active' href='/guix/log/nix/libstore/optimise-store.cc?showmsg=1'>log</a><a href='/guix/tree/nix/libstore/optimise-store.cc?id=41f058d10d17802632a1354eb02dd363057ded4b'>tree</a><a href='/guix/commit/nix/libstore/optimise-store.cc?id=41f058d10d17802632a1354eb02dd363057ded4b'>commit</a><a href='/guix/diff/nix/libstore/optimise-store.cc?id=41f058d10d17802632a1354eb02dd363057ded4b'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/nix/libstore/optimise-store.cc'>
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</select>
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</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=41f058d10d17802632a1354eb02dd363057ded4b&amp;showmsg=1'>root</a>/<a href='/guix/log/nix?id=41f058d10d17802632a1354eb02dd363057ded4b&amp;showmsg=1'>nix</a>/<a href='/guix/log/nix/libstore?id=41f058d10d17802632a1354eb02dd363057ded4b&amp;showmsg=1'>libstore</a>/<a href='/guix/log/nix/libstore/optimise-store.cc?id=41f058d10d17802632a1354eb02dd363057ded4b&amp;showmsg=1'>optimise-store.cc</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/nix/libstore/optimise-store.cc?id=41f058d10d17802632a1354eb02dd363057ded4b'>Collapse</a>)</th><th class='left'>Author</th></tr>
<tr class='logheader'><td><span title='2020-06-25 12:29:22 +0200'>2020-06-25</span></td><td class='logsubject'><a href='/guix/commit/nix/libstore/optimise-store.cc?id=b930f0ba2115f71c323d4bf3d72efb763f716296'>daemon: Correctly handle EMLINK corner case when deduplicating.</a></td><td>Ludovic Courtès</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
Suggested by Caleb Ristvedt &lt;caleb.ristvedt@cune.org&gt;.

* nix/libstore/optimise-store.cc (LocalStore::optimisePath_): Save errno
from 'rename' before calling 'unlink'.


</td></tr>
<tr class='logheader'><td><span title='2019-03-13 23:12:43 +0100'>2019-03-13</span></td><td class='logsubject'><a href='/guix/commit/nix/libstore/optimise-store.cc?id=59e80445882f8b0379e54916f89510c0deda6698'>Remove traces of "GuixSD".</a></td><td>Ludovic Courtès</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
* gnu/bootloader/extlinux.scm (extlinux-configuration-file): Remove
mentions of "GuixSD".
* gnu/bootloader/grub.scm (install-grub-efi): Likewise.
* gnu/build/vm.scm (make-iso9660-image): Change default #:volume-id to
"Guix_image".
(initialize-hard-disk): Search for the "Guix_image" label.
* gnu/ci.scm (system-test-jobs, tarball-jobs): Remove "GuixSD".
* gnu/installer/newt/welcome.scm (run-welcome-page): Likewise.
* gnu/packages/audio.scm (supercollider)[description]: Likewise.
* gnu/packages/curl.scm (curl): Likewise.
* gnu/packages/emacs.scm (emacs): Likewise.
* gnu/packages/gnome.scm (network-manager): Likewise.
* gnu/packages/julia.scm (julia): Likewise.
* gnu/packages/linux.scm (alsa-plugins): Likewise.
(powertop, wireless-regdb): Likewise.
* gnu/packages/package-management.scm (guix): Likewise.
* gnu/packages/polkit.scm (polkit): Likewise.
* gnu/packages/tex.scm (texlive-bin): Likewise.
* gnu/services/base.scm (file-systems-&gt;fstab): Likewise.
* gnu/services/cups.scm (%cups-activation): Likewise.
* gnu/services/mail.scm (%dovecot-activation): Likewise.
* gnu/services/messaging.scm (prosody-configuration)[log]: Likewise.
* gnu/system/examples/vm-image.tmpl (vm-image-motd): Likewise.
* gnu/system/install.scm (installation-os)[file-systems]: Change root
file system label to "Guix_image".
* gnu/system/mapped-devices.scm (check-device-initrd-modules):
Remove "GuixSD".
* gnu/system/vm.scm (system-docker-image): Likewise.
(system-disk-image)[root-label]: Change to "Guix_image".
* gnu/tests/install.scm (run-install): Remove "GuixSD".
* guix/modules.scm (guix-module-name?): Likewise.
* nix/libstore/optimise-store.cc: Likewise.


</td></tr>
<tr class='logheader'><td><span title='2018-12-16 16:28:07 +0100'>2018-12-16</span></td><td class='logsubject'><a href='/guix/commit/nix/libstore/optimise-store.cc?id=8327e733966cc4a93dfaadd1a761ca1088078baa'>daemon: Use unbranded phrases in comments and messages.</a></td><td>Ludovic Courtès</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
* nix/libstore/build.cc, nix/libstore/globals.cc,
nix/libstore/gc.cc, nix/libstore/local-store.cc,
nix/libstore/optimise-store.cc, nix/libstore/store-api.cc,
nix/libutil/archive.cc, nix/nix-daemon/nix-daemon.cc: Replace "Nix
store" by "store", and "Nix daemon" by "build daemon".


</td></tr>