runtime: adjust timediv to avoid _vasop; mark _subv okay

R=dvyukov
CC=golang-dev
https://golang.org/cl/12028046

src/pkg/runtime/runtime.c

@@ -429,7 +429,7 @@ runtime·timediv(int64 v, int32 div, int32 *rem)
 	res = 0;
 	for(bit = 0x40000000; bit != 0; bit >>= 1) {
 		if(v >= (int64)bit*div) {
-			v -= (int64)bit*div;
+			v = v - (int64)bit*div;
 			res += bit;
 		}
 	}

src/pkg/runtime/vlrt_arm.c

@@ -66,27 +66,20 @@ void    runtime·abort(void);
 void
 _addv(Vlong *r, Vlong a, Vlong b)
 {
-	ulong lo, hi;
-
-	lo = a.lo + b.lo;
-	hi = a.hi + b.hi;
-	if(lo < a.lo)
-		hi++;
-	r->lo = lo;
-	r->hi = hi;
+	r->lo = a.lo + b.lo;
+	r->hi = a.hi + b.hi;
+	if(r->lo < a.lo)
+		r->hi++;
 }
 
+#pragma textflag 7
 void
 _subv(Vlong *r, Vlong a, Vlong b)
 {
-	ulong lo, hi;
-
-	lo = a.lo - b.lo;
-	hi = a.hi - b.hi;
-	if(lo > a.lo)
-		hi--;
-	r->lo = lo;
-	r->hi = hi;
+	r->lo = a.lo - b.lo;
+	r->hi = a.hi - b.hi;
+	if(r->lo > a.lo)
+		r->hi--;
 }
 
 void