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6c: copy all of packed structs in OAS

code assumed struct was aligned to atleast LONG.
For packed structs we need to copy the reaminder as well.
Repro:

typedef struct {
	char	a;
	char	b;
	short	c;
	short	d;
	char	e;
	char	f;
	char	g;
	char	h;
} A;

void
main(int argc, char **argv)
{
	A a1, a2;

	a2.a = 1;
	a2.b = 2;
	a2.c = 3;
	a2.d = 4;
	a2.e = 5;
	a2.f = 6;
	a2.g = 7;
	a2.h = 8;

	a1 = a2;
	print("%d %d %d %d %d %d %d %d\n", a1.a, a1.b, a1.c, a1.d, a1.e, a1.f, a1.g, a1.h);
}

--- a/sys/src/cmd/6c/cgen.c

+++ b/sys/src/cmd/6c/cgen.c

@@ -1400,7 +1400,7 @@

 	Prog *p1;

 	Node nod0, nod1, nod2, nod3, nod4, *l, *r;

 	Type *t;

-	int v, c, mt, mo;

+	int v, c, mt, mo, re;

 	vlong o0, o1;

 	if(n == Z || n->type == T)

@@ -1683,6 +1683,7 @@

 		}

 		o0 = n->xoffset;

 		o1 = nn->xoffset;

+		re = w % ewidth[mt];

 		w /= ewidth[mt];

 		while(--w >= 0) {

 			gins(mo, n, &nod0);

@@ -1689,6 +1690,12 @@

 			gins(mo, &nod0, nn);

 			n->xoffset += ewidth[mt];

 			nn->xoffset += ewidth[mt];

+		}

+		while(--re >= 0) {

+			gins(AMOVB, n, &nod0);

+			gins(AMOVB, &nod0, nn);

+			n->xoffset += 1;

+			nn->xoffset += 1;

 		}

 		n->xoffset = o0;

 		nn->xoffset = o1;