Merge branch 'smp-ci' into 'master'

Enable SMP for testing

See merge request redox-os/relibc!1273

check.sh

@@ -106,8 +106,6 @@ run_redoxer() {
         redoxer toolchain || { echo -e "${RED}Fail: redoxer toolchain for: $target.${NC}" && exit 1; }
         export CARGO_TEST="redoxer"
         export TEST_RUNNER="redoxer exec --folder ../../sysroot/$TARGET/:/usr --folder . --"
-# TODO: Identify hang issue with pthread/barrier and pthread/once tests in multi core to get rid of this limit
-        export REDOXER_QEMU_ARGS="-smp 1"
 
         MAKE_ACTION="$MAKE_ACTION IS_REDOX=1"
     else