webengine ffmpeg doesn't build on Qt 5.8.0 on Raspberry Pi

Hi,

Building the latest qt 5.8.0 beta source tarball for a raspberry pi gives the following error during webengine build :

[2054/12237] CC obj/src/3rdparty/chromium/third_party/ffmpeg/libavcodec/ffmpeg.vp8.o
FAILED: obj/src/3rdparty/chromium/third_party/ffmpeg/libavcodec/ffmpeg.vp8.o
/home/longchair/LibreELEC.tv/build.PlexMediaPlayer-RPi2.arm-8.0-devel/toolchain/bin/armv7ve-libreelec-linux-gnueabi-gcc -MMD -MF obj/src/3rdparty/chromium/third_party/ffmpeg/libavcodec/ffmpeg.vp8.o.d -DV8_DEPRECATION_WARNINGS -DTOOLKIT_QT -D_FILE_OFFSET_BITS=64 -DNO_TCMALLOC -DDISABLE_NACL -DGL_GLEXT_PROTOTYPES -DEGL_EGLEXT_PROTOTYPES '-DOPENSSLDIR="/usr/lib/ssl"' -DOPENSSL_LOAD_CONF -DEGL_API_FB=1 -DLINUX=1 -DCHROMIUM_BUILD -DUI_COMPOSITOR_IMAGE_TRANSPORT -DUSE_AURA=1 -DUSE_OZONE=1 -DUSE_DEFAULT_RENDER_THEME=1 -DUSE_LIBJPEG_TURBO=1 -DENABLE_MEDIA_ROUTER=1 -DFIELDTRIAL_TESTING_ENABLED -DENABLE_SPELLCHECK=1 -DENABLE_SUPERVISED_USERS=1 -DENABLE_MDNS=1 -DENABLE_SERVICE_DISCOVERY=1 -DHAVE_AV_CONFIG_H -D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600 -DPIC -DFF_API_CONVERGENCE_DURATION=0 -D_ISOC99_SOURCE -D_LARGEFILE_SOURCE -DUSE_OPENSSL_CERTS=1 -DNDEBUG -DNO_UNWIND_TABLES -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 '-DQTWEBENGINEPROCESS_NAME="QtWebEngineProcess"' -Igen -I/home/longchair/LibreELEC.tv/build.PlexMediaPlayer-RPi2.arm-8.0-devel/qt5-5.8.0-beta/qtwebengine/src/3rdparty/chromium/third_party/ffmpeg/chromium/config/Chromium/linux/arm-neon -I/home/longchair/LibreELEC.tv/build.PlexMediaPlayer-RPi2.arm-8.0-devel/qt5-5.8.0-beta/qtwebengine/src/3rdparty/chromium/third_party/ffmpeg -I/home/longchair/LibreELEC.tv/build.PlexMediaPlayer-RPi2.arm-8.0-devel/toolchain/armv7ve-libreelec-linux-gnueabi/sysroot/opt/vc/include -I/home/longchair/LibreELEC.tv/build.PlexMediaPlayer-RPi2.arm-8.0-devel/toolchain/armv7ve-libreelec-linux-gnueabi/sysroot/opt/vc/include/interface/vcos/pthreads -I/home/longchair/LibreELEC.tv/build.PlexMediaPlayer-RPi2.arm-8.0-devel/toolchain/armv7ve-libreelec-linux-gnueabi/sysroot/opt/vc/include/interface/vmcs_host/linux -fstack-protector --param=ssp-buffer-size=4 -pthread -fno-strict-aliasing -Wno-extra -Wno-unused-parameter -Wno-missing-field-initializers -fvisibility=hidden -pipe -fPIC -Wno-unused-local-typedefs -fPIC -fomit-frame-pointer -Wno-deprecated-declarations -w -DHAVE_VFP_ARGS=1 -std=c99 -pthread -fno-math-errno -fno-signed-zeros -fno-tree-vectorize -Wno-maybe-uninitialized -march=armv7-a -mtune=cortex-a7 -mfpu=neon-vfpv4 -mfloat-abi=hard --sysroot=/home/longchair/LibreELEC.tv/build.PlexMediaPlayer-RPi2.arm-8.0-devel/toolchain/armv7ve-libreelec-linux-gnueabi/sysroot -Os -fno-ident -fdata-sections -ffunction-sections -fno-unwind-tables -fno-asynchronous-unwind-tables -g -c /home/longchair/LibreELEC.tv/build.PlexMediaPlayer-RPi2.arm-8.0-devel/qt5-5.8.0-beta/qtwebengine/src/3rdparty/chromium/third_party/ffmpeg/libavcodec/vp8.c -o obj/src/3rdparty/chromium/third_party/ffmpeg/libavcodec/ffmpeg.vp8.o

Unknown macro: {standard input}

: Assembler messages:

:64: Error: bad instruction `ldrhcs r6,[ip],#2'

Unknown macro: {standard input}

:148: Error: bad instruction `ldrhcs r6,[lr],#2'
[2063/12237] CC obj/src/3rdparty/chromium/third_party/ffmpeg/libavformat/ffmpeg.autorename_libavformat_utils.o
ninja: build stopped: subcommand failed.
Makefile.gyp_run:608: recipe for target 'invoke_ninja' failed
make[5]: *** [invoke_ninja] Error 1

Same build in qt 5.7.0 was working fine