Thanks for posting this! This was the solution I needed to move forward.
With this, I was finally able to build all of MQX, and the PSP lib in particular using ARM DS-5 v5.17.1. (This was for MQX 4.0.2).
Below are the old assembler command line flags wrt the include paths, vs the new ones. I've also attached a screenshot on where to mod these settings in the PSP project file.
OLD: -I"${ProjDirPath}/../../../../mqx/source/tad" -I"${ProjDirPath}/../../../../mqx/source/psp/cortex_a/cpu" -I"${ProjDirPath}/../../../../mqx/source/psp/cortex_a/compiler/rv_ds5" -I"${ProjDirPath}/../../../../mqx/source/psp/cortex_a" -I"${ProjDirPath}/../../../../mqx/source/io/usb" -I"${ProjDirPath}/../../../../mqx/source/io/tfs" -I"${ProjDirPath}/../../../../mqx/source/io/spi" -I"${ProjDirPath}/../../../../mqx/source/io/serial" -I"${ProjDirPath}/../../../../mqx/source/io/sdcard/sdcard_esdhc" -I"${ProjDirPath}/../../../../mqx/source/io/sdcard" -I"${ProjDirPath}/../../../../mqx/source/io/sai/int" -I"${ProjDirPath}/../../../../mqx/source/io/sai" -I"${ProjDirPath}/../../../../mqx/source/io/rtc" -I"${ProjDirPath}/../../../../mqx/source/io/qspi" -I"${ProjDirPath}/../../../../mqx/source/io/pipe" -I"${ProjDirPath}/../../../../mqx/source/io/pcb/shmem" -I"${ProjDirPath}/../../../../mqx/source/io/pcb/mqxa" -I"${ProjDirPath}/../../../../mqx/source/io/pcb" -I"${ProjDirPath}/../../../../mqx/source/io/nandflash/nfc" -I"${ProjDirPath}/../../../../mqx/source/io/nandflash" -I"${ProjDirPath}/../../../../mqx/source/io/lwgpio" -I"${ProjDirPath}/../../../../mqx/source/io/lwadc" -I"${ProjDirPath}/../../../../mqx/source/io/io_null" -I"${ProjDirPath}/../../../../mqx/source/io/io_mem" -I"${ProjDirPath}/../../../../mqx/source/io/io_dun" -I"${ProjDirPath}/../../../../mqx/source/io/i2c/polled" -I"${ProjDirPath}/../../../../mqx/source/io/i2c/int" -I"${ProjDirPath}/../../../../mqx/source/io/i2c" -I"${ProjDirPath}/../../../../mqx/source/io/hwtimer" -I"${ProjDirPath}/../../../../mqx/source/io/esdhc" -I"${ProjDirPath}/../../../../mqx/source/io/enet/phy" -I"${ProjDirPath}/../../../../mqx/source/io/enet/macnet" -I"${ProjDirPath}/../../../../mqx/source/io/enet" -I"${ProjDirPath}/../../../../mqx/source/io/dma" -I"${ProjDirPath}/../../../../mqx/source/io/core_mutex" -I"${ProjDirPath}/../../../../mqx/source/io/cm" -I"${ProjDirPath}/../../../../mqx/source/include" -I"${ProjDirPath}/../../../../mqx/source/bsp/twrvf65gs10_a5" -I"${ProjDirPath}/../../../../config/twrvf65gs10_a5" -I"${ProjDirPath}/../../../../config/common" -I"${ds5_install_path}/include"'
NEW: -i"${ProjDirPath}/../../../../mqx/source/tad","${ProjDirPath}/../../../../mqx/source/psp/cortex_a/cpu","${ProjDirPath}/../../../../mqx/source/psp/cortex_a/compiler/rv_ds5","${ProjDirPath}/../../../../mqx/source/psp/cortex_a","${ProjDirPath}/../../../../mqx/source/io/usb","${ProjDirPath}/../../../../mqx/source/io/tfs","${ProjDirPath}/../../../../mqx/source/io/spi","${ProjDirPath}/../../../../mqx/source/io/serial","${ProjDirPath}/../../../../mqx/source/io/sdcard/sdcard_esdhc","${ProjDirPath}/../../../../mqx/source/io/sdcard","${ProjDirPath}/../../../../mqx/source/io/sai/int","${ProjDirPath}/../../../../mqx/source/io/sai","${ProjDirPath}/../../../../mqx/source/io/rtc","${ProjDirPath}/../../../../mqx/source/io/qspi","${ProjDirPath}/../../../../mqx/source/io/pipe","${ProjDirPath}/../../../../mqx/source/io/pcb/shmem","${ProjDirPath}/../../../../mqx/source/io/pcb/mqxa","${ProjDirPath}/../../../../mqx/source/io/pcb","${ProjDirPath}/../../../../mqx/source/io/nandflash/nfc","${ProjDirPath}/../../../../mqx/source/io/nandflash","${ProjDirPath}/../../../../mqx/source/io/lwgpio","${ProjDirPath}/../../../../mqx/source/io/lwadc","${ProjDirPath}/../../../../mqx/source/io/io_null","${ProjDirPath}/../../../../mqx/source/io/io_mem","${ProjDirPath}/../../../../mqx/source/io/io_dun","${ProjDirPath}/../../../../mqx/source/io/i2c/polled","${ProjDirPath}/../../../../mqx/source/io/i2c/int","${ProjDirPath}/../../../../mqx/source/io/i2c","${ProjDirPath}/../../../../mqx/source/io/hwtimer","${ProjDirPath}/../../../../mqx/source/io/esdhc","${ProjDirPath}/../../../../mqx/source/io/enet/phy","${ProjDirPath}/../../../../mqx/source/io/enet/macnet","${ProjDirPath}/../../../../mqx/source/io/enet","${ProjDirPath}/../../../../mqx/source/io/dma","${ProjDirPath}/../../../../mqx/source/io/core_mutex","${ProjDirPath}/../../../../mqx/source/io/cm","${ProjDirPath}/../../../../mqx/source/include","${ProjDirPath}/../../../../mqx/source/bsp/twrvf65gs10_a5","${ProjDirPath}/../../../../config/twrvf65gs10_a5","${ProjDirPath}/../../../../config/common","${ds5_install_path}/include"