buildsys: fix IS_IN_lib* for .s
buildsys: fix IS_IN_lib* for .s

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

brgl/uclibc-ng,wbx-github/uclibc-ng,kraj/uclibc-ng,majek/uclibc-vx32,foss-for-synopsys-dwc-arc-processors/uClibc,brgl/uclibc-ng,kraj/uClibc,kraj/uclibc-ng,kraj/uClibc,wbx-github/uclibc-ng,foss-for-synopsys-dwc-arc-processors/uClibc,kraj/uClibc,majek/uclibc-vx32,wbx-github/uclibc-ng,majek/uclibc-vx32,brgl/uclibc-ng,majek/uclibc-vx32,kraj/uclibc-ng,wbx-github/uclibc-ng,foss-for-synopsys-dwc-arc-processors/uClibc,foss-for-synopsys-dwc-arc-processors/uClibc,kraj/uclibc-ng,kraj/uClibc,brgl/uclibc-ng