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}

ix</a></td><td class='form'><form method='get'>
<input type='hidden' name='id' value='eee86c6e5bd99102aa08d0c9be4407738abeb10d'/><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>
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<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=eee86c6e5bd99102aa08d0c9be4407738abeb10d'>refs</a><a class='active' href='/guix/log/tests/guix-repl.sh'>log</a><a href='/guix/tree/tests/guix-repl.sh?id=eee86c6e5bd99102aa08d0c9be4407738abeb10d'>tree</a><a href='/guix/commit/tests/guix-repl.sh?id=eee86c6e5bd99102aa08d0c9be4407738abeb10d'>commit</a><a href='/guix/diff/tests/guix-repl.sh?id=eee86c6e5bd99102aa08d0c9be4407738abeb10d'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/tests/guix-repl.sh'>
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<div class='path'>path: <a href='/guix/log/?id=eee86c6e5bd99102aa08d0c9be4407738abeb10d'>root</a>/<a href='/guix/log/tests?id=eee86c6e5bd99102aa08d0c9be4407738abeb10d'>tests</a>/<a href='/guix/log/tests/guix-repl.sh?id=eee86c6e5bd99102aa08d0c9be4407738abeb10d'>guix-repl.sh</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/tests/guix-repl.sh?id=eee86c6e5bd99102aa08d0c9be4407738abeb10d&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-09-16 16:04:01 +0200'>2020-09-16</span></td><td><a href='/guix/commit/tests/guix-repl.sh?id=d7f7ed39be3be926b3c46c0ea15d416c593ef61f'>repl: Look for script files in (getcwd).</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://bugs.gnu.org/43331&gt;.

* guix/scripts/repl.scm (guix-repl): Replace "." by (getcwd)
* tests/guix-repl.sh: Add test.

Co-authored-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Konrad Hinsen</td></tr>
<tr><td><span title='2020-06-14 23:02:36 +0200'>2020-06-14</span></td><td><a href='/guix/commit/tests/guix-repl.sh?id=c924e541390f9595d819edc33c19d979917c15ec'>guix repl: Add script execution.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/repl.scm: Add filename options for script execution.
* doc/guix.texi (Invoking guix repl): Document it.
* tests/guix-repl.sh: Test it.
* Makefile.am: (SH_TESTS): Add it.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Konrad Hinsen</td></tr>