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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<tr><td><span title='2019-02-13 05:42:58 +0100'>2019-02-13</span></td><td><a href='/guix/commit/gnu/packages/aidc.scm?id=0e249bdecf7fbd3d1e8ee9598538f72f87dba854'>gnu: libdmtx: Edit description.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2019-02-13 05:42:58 +0100'>2019-02-13</span></td><td><a href='/guix/commit/gnu/packages/aidc.scm?id=b9a807b7b8262fec8a00c8bf99445bf1db71828a'>gnu: libdmtx: Update to 0.7.5.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2018-06-14 18:55:51 +0200'>2018-06-14</span></td><td><a href='/guix/commit/gnu/packages/aidc.scm?id=6dd5f2ea634107625831fbd36fb313df5c3c79d6'>gnu: qrencode: Update to 4.0.2.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2018-05-04 21:46:16 -0400'>2018-05-04</span></td><td><a href='/guix/commit/gnu/packages/aidc.scm?id=d3cd435709b20a6a8358e06afe959f6a24adb29a'>gnu: qrencode: Update to 4.0.0.</a><span class='msg-avail'>...</span></td><td>Kei Kebreau</td></tr>