libubacktrace: fix makefile clean target
libubacktrace: fix makefile clean target

Fix makefile lean target removing the old reference to the non
existing libubacktrace_ARCH_OUT variable.

Signed-off-by: Carmelo Amoroso <532378793705a04edd56deb76ad8c0442834d55d@st.com>

ffainelli/uClibc,groundwater/uClibc,skristiansson/uClibc-or1k,atgreen/uClibc-moxie,ddcc/klee-uclibc-0.9.33.2,brgl/uclibc-ng,ndmsystems/uClibc,hjl-tools/uClibc,atgreen/uClibc-moxie,kraj/uclibc-ng,atgreen/uClibc-moxie,mephi42/uClibc,brgl/uclibc-ng,ddcc/klee-uclibc-0.9.33.2,mephi42/uClibc,mephi42/uClibc,hjl-tools/uClibc,groundwater/uClibc,skristiansson/uClibc-or1k,majek/uclibc-vx32,wbx-github/uclibc-ng,brgl/uclibc-ng,ffainelli/uClibc,kraj/uclibc-ng,waweber/uclibc-clang,majek/uclibc-vx32,ffainelli/uClibc,wbx-github/uclibc-ng,foss-for-synopsys-dwc-arc-processors/uClibc,foss-for-synopsys-dwc-arc-processors/uClibc,waweber/uclibc-clang,mephi42/uClibc,brgl/uclibc-ng,kraj/uClibc,groundwater/uClibc,hjl-tools/uClibc,groundwater/uClibc,foss-for-synopsys-dwc-arc-processors/uClibc,m-labs/uclibc-lm32,ndmsystems/uClibc,czankel/xtensa-uclibc,m-labs/uclibc-lm32,hwoarang/uClibc,wbx-github/uclibc-ng,groundwater/uClibc,foss-xtensa/uClibc,ddcc/klee-uclibc-0.9.33.2,ffainelli/uClibc,ffainelli/uClibc,ddcc/klee-uclibc-0.9.33.2,foss-xtensa/uClibc,m-labs/uclibc-lm32,czankel/xtensa-uclibc,kraj/uclibc-ng,skristiansson/uClibc-or1k,kraj/uClibc,foss-xtensa/uClibc,foss-for-synopsys-dwc-arc-processors/uClibc,m-labs/uclibc-lm32,hjl-tools/uClibc,foss-xtensa/uClibc,ndmsystems/uClibc,hwoarang/uClibc,wbx-github/uclibc-ng,waweber/uclibc-clang,kraj/uClibc,czankel/xtensa-uclibc,waweber/uclibc-clang,kraj/uClibc,hwoarang/uClibc,majek/uclibc-vx32,atgreen/uClibc-moxie,majek/uclibc-vx32,czankel/xtensa-uclibc,hjl-tools/uClibc,kraj/uclibc-ng,hwoarang/uClibc,skristiansson/uClibc-or1k,ndmsystems/uClibc