optimize away the conditional in arrow_step since OTAWA says it is slightly better

include/arrow.h

@@ -27,11 +27,9 @@ extern void _arrow_dealloc (struct _arrow_mem *);
 #define _arrow_reset(self) {(self)->_reg._first = 1;}
 
 inline _Bool _arrow_step(struct _arrow_mem *self) {
-  if (self->_reg._first) {
-    self->_reg._first = 0;
-    return 1;
-  }
-  return 0;
+  _Bool old = self->_reg._first;
+  self->_reg._first = 0;
+  return old;
 }
 
 #endif

include/arrow_spec.h

@@ -67,12 +67,10 @@ extern void _arrow_dealloc (struct _arrow_mem *);
 inline _Bool _arrow_step(struct _arrow_mem *self)
        /*@ ghost (struct _arrow_mem_ghost \ghost *mem) */
 {
-  if (self->_reg._first) {
-    self->_reg._first = 0;
-    //@ ghost mem->_reg._first = 0;
-    return 1;
-  }
-  return 0;
+  _Bool old = self->_reg._first;
+  self->_reg._first = 0;
+  //@ ghost mem->_reg._first = 0;
+  return old;
 }
 
 /*@ ghost