Ah ha, I was missing some flags. I think I’ve got that sorted out now, but I’m hitting a snag with includes:
cd /Users/kamil/xxx/Project/sbuild/haldrivers && /Users/kamil/tmp/clang+llvm-10.0.0-x86_64-apple-darwin/bin/clang++ --sysroot=/usr/local/Cellar/arm-none-eabi-gcc/9-2019-q4-major/gcc/bin/../arm-none-eabi -DARM -DSTM32F401VETx -DSTM32F401xC -DSTM32F4xx -DUSE_FULL_LL_DRIVER -I/Users/kamil/xxx/lib/haldrivers/.. -I/Users/kamil/xxx/lib/haldrivers/../../Drivers/STM32_USB_Device_Library/Core/Inc -I/Users/kamil/xxx/lib/haldrivers/usb_midi -I/Users/kamil/xxx/lib/haldrivers/../lib -I/Users/kamil/xxx/cmake/../Drivers/STM32F4xx_HAL_Driver/Inc -I/Users/kamil/xxx/Project/Inc -I/Users/kamil/xxx/cmake/../Drivers/CMSIS/Device/ST/STM32F4xx/Include -I/Users/kamil/xxx/cmake/../Drivers/CMSIS/CMSIS/Include -Og -fno-exceptions -DDEBUG -g -gdwarf-2 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -mcpu=cortex-m4 -fdata-sections -ffunction-sections -mthumb --target=arm-none-eabi -fno-rtti -Wno-register -Wall -std=gnu++17 -o CMakeFiles/haldrivers.dir/assert.cpp.o -c /Users/kamil/xxx/lib/haldrivers/assert.cpp
/Users/kamil/xxx/lib/haldrivers/assert.cpp:1:10: fatal error: 'cstdint' file not found