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}

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<div class='path'>path: <a href='/guix/log/?id=389cae8b0727bff958e4a2dd98526cf7edbe9ade'>root</a>/<a href='/guix/log/gnu?id=389cae8b0727bff958e4a2dd98526cf7edbe9ade'>gnu</a>/<a href='/guix/log/gnu/bootloader.scm?id=389cae8b0727bff958e4a2dd98526cf7edbe9ade'>bootloader.scm</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/gnu/bootloader.scm?id=389cae8b0727bff958e4a2dd98526cf7edbe9ade&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-08-30 01:33:45 +0200'>2019-08-30</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=a28cfee841e9c5ab179291d3065f1486fd065e7e'>system: Add 'bootloader-menu-entries' field to &lt;boot-parameters&gt;.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-08-30 01:33:45 +0200'>2019-08-30</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=ac9cd78ea9e6a3cf850b33fb2111b85e2bbf533d'>bootloader: Fix comment about 'menu-entries'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-03-24 23:06:11 +0100'>2019-03-24</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=8d058e7b1b1a409d3d9cc29c5650a98db4e78783'>bootloader: Add a 'keyboard-layout' field.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-03-24 23:06:10 +0100'>2019-03-24</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=91b6873b24c205bd445844845fb44add643d0cff'>bootloader: Reindent record type definition.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-03-24 23:06:10 +0100'>2019-03-24</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=8a0e1bb12b3c22a8c9a2be17492058ca63ec7c5d'>bootloader: Remove unused 'additional-configuration' field.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-01-16 14:07:38 +0100'>2019-01-16</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=5f7467f046c3c1648cdf6eb81b3ec041bfc1f9bb'>bootloader: Remove deprecated 'device' field.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-04-08 17:48:33 +0200'>2018-04-08</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=3c0128b035ae00462f1b0a4427d9525d750e5575'>discovery: Remove dependency on (guix ui).</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-08-28 09:56:33 +0200'>2017-08-28</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=9e1fe3d0c34e65a50ba93b5d7f7398503131c1ba'>bootloader: Emit warnings with 'warning'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-08-23 22:23:19 +0200'>2017-08-23</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=045ebb3e58d74c75f39ce47380045d3cd00359c3'>gnu: bootloader: Deprecate "device" field in favor of "target".</a><span class='msg-avail'>...</span></td><td>Andy Wingo</td></tr>
<tr><td><span title='2017-07-28 21:56:18 +0200'>2017-07-28</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=1975c754f487eb4933724ca3b116442d21ef8dd9'>bootloader: Use &lt;menu-entry&gt; for the bootloader side.</a><span class='msg-avail'>...</span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2017-06-08 16:29:29 +0200'>2017-06-08</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=8b22107e5d0bdeb300fb33b5a40aed2057a66b94'>bootloader: Use menu-entry to define custom bootloader entries.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2017-05-16 14:41:01 +0200'>2017-05-16</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=b09a8da4a2e50845a297e041762f3ff9e649c047'>bootloader: Add extlinux support.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>