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=170436771968dfa272225ea45b63689b900fd317'>root</a>/<a href='/guix/log/gnu?id=170436771968dfa272225ea45b63689b900fd317'>gnu</a>/<a href='/guix/log/gnu/packages?id=170436771968dfa272225ea45b63689b900fd317'>packages</a>/<a href='/guix/log/gnu/packages/patches?id=170436771968dfa272225ea45b63689b900fd317'>patches</a>/<a href='/guix/log/gnu/packages/patches/gcc-4.9-libsanitizer-fix.patch?id=170436771968dfa272225ea45b63689b900fd317'>gcc-4.9-libsanitizer-fix.patch</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/packages/patches/gcc-4.9-libsanitizer-fix.patch?id=170436771968dfa272225ea45b63689b900fd317&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2018-02-18 00:48:16 +0100'>2018-02-18</span></td><td><a href='/guix/commit/gnu/packages/patches/gcc-4.9-libsanitizer-fix.patch?id=d65930708f1a55d9c1ecdb53e189d154902b0f05'>gnu: gcc@4.9: Fix libsanitizer compilation with glibc 2.26.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>