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=fdae245a753d77a8266764fdcc8e11434a57d046'>root</a>/<a href='/guix/log/etc?id=fdae245a753d77a8266764fdcc8e11434a57d046'>etc</a>/<a href='/guix/log/etc/disarchive-manifest.scm?id=fdae245a753d77a8266764fdcc8e11434a57d046'>disarchive-manifest.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/etc/disarchive-manifest.scm?id=fdae245a753d77a8266764fdcc8e11434a57d046&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-10-09 01:02:18 +0200'>2021-10-09</span></td><td><a href='/guix/commit/etc/disarchive-manifest.scm?id=2ad1ef844632b7605ad6dd362e947a122a0a3925'>disarchive-manifest: Provide valid 'version' string.</a><span class='msg-avail'>...<span class='msg-tooltip'>* etc/disarchive-manifest.scm &lt;top level&gt;: Turn 'version' field into a
string.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-09-14 11:50:58 +0200'>2021-09-14</span></td><td><a href='/guix/commit/etc/disarchive-manifest.scm?id=98712c14fe3517a48603a12eb2e64db305a54fe5'>etc: Add 'disarchive-manifest.scm'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* etc/disarchive-manifest.scm: New file.
* Makefile.am (EXTRA_DIST): Add it.
</span></span></td><td>Ludovic Courtès</td></tr>