sleep: add comment with test program for SIG_IGNed SIGCHLD
sleep: add comment with test program for SIG_IGNed SIGCHLD

Signed-off-by: Denys Vlasenko <42afb3a19136e88700e8b77002ea6a5a94c16782@googlemail.com>

atgreen/uClibc-moxie,groundwater/uClibc,brgl/uclibc-ng,ddcc/klee-uclibc-0.9.33.2,kraj/uclibc-ng,hwoarang/uClibc,ffainelli/uClibc,foss-for-synopsys-dwc-arc-processors/uClibc,ndmsystems/uClibc,foss-for-synopsys-dwc-arc-processors/uClibc,czankel/xtensa-uclibc,wbx-github/uclibc-ng,hjl-tools/uClibc,groundwater/uClibc,majek/uclibc-vx32,ffainelli/uClibc,ffainelli/uClibc,atgreen/uClibc-moxie,brgl/uclibc-ng,atgreen/uClibc-moxie,czankel/xtensa-uclibc,brgl/uclibc-ng,kraj/uclibc-ng,kraj/uClibc,groundwater/uClibc,czankel/xtensa-uclibc,ysat0/uClibc,foss-xtensa/uClibc,ysat0/uClibc,ffainelli/uClibc,ffainelli/uClibc,czankel/xtensa-uclibc,atgreen/uClibc-moxie,hjl-tools/uClibc,foss-xtensa/uClibc,mephi42/uClibc,ndmsystems/uClibc,hwoarang/uClibc,waweber/uclibc-clang,hwoarang/uClibc,foss-for-synopsys-dwc-arc-processors/uClibc,wbx-github/uclibc-ng,foss-for-synopsys-dwc-arc-processors/uClibc,skristiansson/uClibc-or1k,kraj/uClibc,kraj/uClibc,brgl/uclibc-ng,m-labs/uclibc-lm32,m-labs/uclibc-lm32,hwoarang/uClibc,wbx-github/uclibc-ng,skristiansson/uClibc-or1k,skristiansson/uClibc-or1k,majek/uclibc-vx32,ysat0/uClibc,mephi42/uClibc,hjl-tools/uClibc,ddcc/klee-uclibc-0.9.33.2,m-labs/uclibc-lm32,kraj/uclibc-ng,waweber/uclibc-clang,skristiansson/uClibc-or1k,ddcc/klee-uclibc-0.9.33.2,kraj/uClibc,waweber/uclibc-clang,ndmsystems/uClibc,foss-xtensa/uClibc,foss-xtensa/uClibc,m-labs/uclibc-lm32,mephi42/uClibc,groundwater/uClibc,ndmsystems/uClibc,hjl-tools/uClibc,groundwater/uClibc,ysat0/uClibc,waweber/uclibc-clang,majek/uclibc-vx32,wbx-github/uclibc-ng,ddcc/klee-uclibc-0.9.33.2,majek/uclibc-vx32,kraj/uclibc-ng,mephi42/uClibc,hjl-tools/uClibc