linker crash in arm stub generation

[Phil Blundell <pb at reciva dot com>]

This testcase causes the linker (CVS head from a couple of days ago,
arm-linuxgnueabi target) to segfault in arm_build_one_stub():

$ cat test1.s
	.cpu arm10tdmi
	.fpu softvfp
	.eabi_attribute 20, 1
	.eabi_attribute 21, 1
	.eabi_attribute 23, 3
	.eabi_attribute 24, 1
	.eabi_attribute 25, 1
	.eabi_attribute 26, 2
	.eabi_attribute 30, 2
	.eabi_attribute 18, 4
	.code	16
	.file	"t.c"
	.text
	.align	2
	.global	foo
	.code	16
	.thumb_func
	.type	foo, %function
foo:
	@ sp needed for prologue
	bx	lr
	.size	foo, .-foo
	.ident	"GCC: (GNU) 4.4.0"
	.section	.note.GNU-stack,"",%progbits
$ cat test2.s
        bl      foo(PLT)
$ ../gas/as-new -o test1.o test1.s
$ ../gas/as-new -o test2.o test2.s
$ ./ld-new -shared -o test1.so test1.o
$ ./ld-new -shared test2.o test1.so
Segmentation fault
$

p.