dynamic linker entry point for arm

mildly tested, seems to work

src/ldso/arm/start.s

@@ -0,0 +1,14 @@
+.text
+.global _start
+_start:
+	ldr r0,[sp]
+	add r1,sp,#4
+	ldr r2,2f
+	add r2,pc,r2
+1:	bl __dynlink
+	mov r1,r0
+	mov r0,#0
+	tst r1,#1
+	moveq pc,r1
+	bx r1
+2:	.word _GLOBAL_OFFSET_TABLE_ - 1b - 4