When trying to build QtWebEngine for a raspberry pi 3 (ARM 32bits), a bunch of host tools are built using C++. Instead of being built directly for my amd64 arch, they are built for x86. My debian sid installation was incomplete, I had gcc-multilib only and was missing at least libstdc++-7-dev:i386 and g++-multilib. A warning from buildroot would be nice since this error occurs after a quite long build time. As discussed on IRC : <gportay> kos_tom: Do you prefer to add a BR2_HOSTARCH_NEEDS_IA32_CXX_COMPILER; or BR2_HOSTARCH_NEEDS_IA32_COMPILER checks for both c and c++ multilib support? <kos_tom> gportay: that is a good question :-) <kos_tom> I would say keep it simple, and just test for C++ support in BR2_HOSTARCH_NEEDS_IA32_COMPILER <gportay> kos_tom: because we do not really want for force installation of c++ multilib when not needed <gportay> okay <kos_tom> but don't hesitate to raise this point in a note in your commit log, so that others can comment Thanks to you guys for the support on IRC :)
Corresponding Qt bug : https://bugreports.qt.io/browse/QTBUG-64869
More globally: qt5webengine will build host tools that are the same bitness as the target, so it is not possible to build for a 64-bit target on a 32-bit host.
There's a patch for this waiting in patchwork: http://patchwork.ozlabs.org/patch/842670/.
Fixed by https://git.buildroot.org/buildroot/commit/?id=27d22296927d7e4ec0965f2bdaa272b1e8ea15e7.