runtime: fix build for ARM

Change-Id: Ia18b8411bebc47ea71ac1acd9ff9dc570ec15dea
Reviewed-on: https://go-review.googlesource.com/2341Reviewed-by: Dave Cheney <dave@cheney.net>

src/runtime/asm_arm.s

@@ -394,7 +394,7 @@ TEXT NAME(SB), WRAPPER, $MAXSIZE-20;		\
 	ADD	R3, R1;				\
 	ADD	R3, R0;				\
 	SUB	R3, R2;				\
-loop:
+loop:						\
 	CMP	$0, R2;				\
 	B.EQ	end;				\
 	MOVBU.P	1(R1), R5;			\

src/runtime/atomic_arm.go

@@ -38,10 +38,10 @@ func xchg(addr *uint32, v uint32) uint32 {
 }
 
 //go:nosplit
-func xchgp1(addr *unsafe.Pointer, v unsafe.Pointer) unsafe.Pointer {
+func xchgp1(addr unsafe.Pointer, v unsafe.Pointer) unsafe.Pointer {
 	for {
-		old := *addr
-		if casp1(addr, old, v) {
+		old := *(*unsafe.Pointer)(addr)
+		if casp1((*unsafe.Pointer)(addr), old, v) {
 			return old
 		}
 	}