help: Document CROSS=
help: Document CROSS=

should maybe better read "override CROSS_COMPILE from above"

Signed-off-by: Bernhard Reutner-Fischer <ce1ac9e9ad16abccd7821f371ad381197b4768ac@gmail.com>

wbx-github/uclibc-ng,brgl/uclibc-ng,czankel/xtensa-uclibc,foss-xtensa/uClibc,skristiansson/uClibc-or1k,kraj/uClibc,hwoarang/uClibc,brgl/uclibc-ng,wbx-github/uclibc-ng,wbx-github/uclibc-ng,foss-xtensa/uClibc,majek/uclibc-vx32,waweber/uclibc-clang,foss-xtensa/uClibc,ddcc/klee-uclibc-0.9.33.2,skristiansson/uClibc-or1k,mephi42/uClibc,waweber/uclibc-clang,mephi42/uClibc,groundwater/uClibc,mephi42/uClibc,ddcc/klee-uclibc-0.9.33.2,foss-for-synopsys-dwc-arc-processors/uClibc,majek/uclibc-vx32,czankel/xtensa-uclibc,czankel/xtensa-uclibc,brgl/uclibc-ng,hjl-tools/uClibc,groundwater/uClibc,ddcc/klee-uclibc-0.9.33.2,brgl/uclibc-ng,hjl-tools/uClibc,hwoarang/uClibc,foss-xtensa/uClibc,hjl-tools/uClibc,ffainelli/uClibc,kraj/uClibc,groundwater/uClibc,skristiansson/uClibc-or1k,ffainelli/uClibc,majek/uclibc-vx32,mephi42/uClibc,kraj/uclibc-ng,kraj/uclibc-ng,groundwater/uClibc,waweber/uclibc-clang,waweber/uclibc-clang,hwoarang/uClibc,skristiansson/uClibc-or1k,kraj/uClibc,kraj/uclibc-ng,hwoarang/uClibc,czankel/xtensa-uclibc,ddcc/klee-uclibc-0.9.33.2,wbx-github/uclibc-ng,ffainelli/uClibc,kraj/uclibc-ng,kraj/uClibc,hjl-tools/uClibc,groundwater/uClibc,ffainelli/uClibc,ffainelli/uClibc,foss-for-synopsys-dwc-arc-processors/uClibc,foss-for-synopsys-dwc-arc-processors/uClibc,hjl-tools/uClibc,foss-for-synopsys-dwc-arc-processors/uClibc,majek/uclibc-vx32