qtwebengine fails to build on aarch64 because of duplicate defines inside chromium

I am building qt with gcc 5.3 on an aarch64 device equipped with a Mali GPU (Odroid C2).

The full build works about right, but there is a build error in webengine near the end

/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/content/gpu/gpu_main.cc -o obj/src/3rdparty/chromium/content/gpu/content_gpu.gpu_main.o
In file included from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/third_party/mesa/src/include/GL/gl.h:2086:0,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/ui/gl/gl_bindings.h:13,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/gpu/command_buffer/service/gl_utils.h:14,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/gpu/command_buffer/service/texture_manager.h:20,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/content/common/gpu/media/gpu_video_decode_accelerator.h:19,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/content/gpu/gpu_main.cc:27:
/home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/third_party/mesa/src/include/GL/glext.h:6156:25: error: conflicting declaration 'typedef long int GLintptr'
typedef signed long int GLintptr;
^
In file included from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/gpu/command_buffer/service/context_group.h:17:0,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/content/common/gpu/gpu_command_buffer_stub.h:24,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/content/common/gpu/media/gpu_video_decode_accelerator.h:18,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/content/gpu/gpu_main.cc:27:
/home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/gpu/command_buffer/common/gles2_cmd_format.h:51:26: note: previous declaration as 'typedef khronos_intptr_t GLintptr'
typedef khronos_intptr_t GLintptr;
^
In file included from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/third_party/mesa/src/include/GL/gl.h:2086:0,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/ui/gl/gl_bindings.h:13,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/gpu/command_buffer/service/gl_utils.h:14,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/gpu/command_buffer/service/texture_manager.h:20,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/content/common/gpu/media/gpu_video_decode_accelerator.h:19,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/content/gpu/gpu_main.cc:27:
/home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/third_party/mesa/src/include/GL/glext.h:6157:25: error: conflicting declaration 'typedef long int GLsizeiptr'
typedef signed long int GLsizeiptr;
^
In file included from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/gpu/command_buffer/service/context_group.h:17:0,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/content/common/gpu/gpu_command_buffer_stub.h:24,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/content/common/gpu/media/gpu_video_decode_accelerator.h:18,
from /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/content/gpu/gpu_main.cc:27:
/home/longchair/LibreELEC.tv/build.PlexMediaPlayer-Odroid_C2.aarch64-7.0-devel/qt-5.7.0-alpha/qtwebengine/src/3rdparty/chromium/gpu/command_buffer/common/gles2_cmd_format.h:52:25: note: previous declaration as 'typedef khronos_ssize_t GLsizeiptr'
typedef khronos_ssize_t GLsizeiptr;
^
ninja: build stopped: subcommand failed.

this issue seems close to this old one https://bugreports.qt.io/browse/QTBUG-44240 but i haven't been able to figure out the right fix. That issue didn't happen with qt 5.6.0