Qt configure not finding header file(s)

[ocgltd]

I am setting up a cross-compile environment, to run on my x86_64 Linux, building for Arm 64 (raspberry). When I configure Qt open source I see;

Note: QtSerialBus: Cannot find linux/can.h and linux/can/raw.h Linux headers for socketCAN support.

I downloaded the full Qt from http://download.qt.io/official_releases/qt/5.15/5.15.2/single/qt-everywhere-src-5.15.2.tar.xz and I made sure my sysroot contains:

~/raspi/sysroot/usr/include/linux/can.h

Why is this not found? My configure command is:

./configure -release -opengl es2 -device linux-rasp-pi3-g++ -device-option CROSS_COMPILE=/root/raspi/arm-gnu-toolchain-12.2.mpacbti-rel1-x86_64-arm-none-eabi/bin/arm-none-eabi- -sysroot ~/raspi/sysroot -opensource -confirm-license -skip qtwayland -skip qtlocation -skip qtscript -make libs -prefix /usr/local/qt5pi -extprefix ~/raspi/qt5pi -hostprefix ~/raspi/qt5 -no-use-gold-linker -v -no-gbm

I tried adding:

INCLUDEPATH += /root/raspi/sysroot/usr/include

to the qmake.conf but it has no effect