8g: fix 386 floating point stack bug

Also fixes issue 310 comment 5 error.
Fixes #310.

R=rsc
https://golang.org/cl/163042

src/cmd/8c/reg.c

@@ -254,7 +254,9 @@ regopt(Prog *p)
 		 */
 		case AFMOVDP:
 		case AFMOVFP:
+		case AFMOVLP:
 		case AFMOVVP:
+		case AFMOVWP:
 		case ACALL:
 			for(z=0; z<BITS; z++)
 				addrs.b[z] |= bit.b[z];

src/cmd/8g/gsubr.c

@@ -1289,10 +1289,12 @@ gmove(Node *f, Node *t)
 		if(t->op == OREGISTER)
 			goto hardmem;
 		nodreg(&r1, types[ft], D_F0);
-		if(ft == TFLOAT32 && f->op != OREGISTER)
+		if(f->op != OREGISTER) {
+			if(ft == TFLOAT32)
 				gins(AFMOVF, f, &r1);
 			else
 				gins(AFMOVD, f, &r1);
+		}
 
 		// set round to zero mode during conversion
 		tempalloc(&t1, types[TUINT16]);

src/cmd/8g/reg.c

@@ -306,8 +306,9 @@ regopt(Prog *firstp)
 		 */
 		case AFMOVDP:
 		case AFMOVFP:
-		case AFMOVVP:
 		case AFMOVLP:
+		case AFMOVVP:
+		case AFMOVWP:
 		case ACALL:
 			for(z=0; z<BITS; z++)
 				addrs.b[z] |= bit.b[z];