Add missing _exit symbol

This is required when `abort()` is linked in, otherwise we get
an unsatisfied symbol.

Signed-off-by: Christophe de Dinechin <[email protected]>

Author: c3d

dmcp/sys/pgm_syscalls.c

@@ -31,7 +31,7 @@ OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 
-  The software and related material is released as “NOMAS”  (NOt MAnufacturer Supported). 
+  The software and related material is released as “NOMAS”  (NOt MAnufacturer Supported).
 
   1. Info is released to assist customers using, exploring and extending the product
   2. Do NOT contact the manufacturer with questions, seeking support, etc. regarding
@@ -171,3 +171,9 @@ void post_main() {
 	sys_reset();
 }
 
+void  __attribute__((__noreturn__)) _exit(int status)
+{
+    set_reset_magic(RUN_DMCP_MAGIC);
+    sys_reset();
+    while(1);
+}