py, unix: Allow to compile with -Wunused-parameter.

See issue #699.
diff --git a/py/asmx86.c b/py/asmx86.c
index 755ed03..11107f1 100644
--- a/py/asmx86.c
+++ b/py/asmx86.c
@@ -145,6 +145,7 @@
 }
 
 void asm_x86_end_pass(asm_x86_t *as) {
+    (void)as;
 }
 
 // all functions must go through this one to emit bytes