pe-mips: refhi/reflo reloc problems

[Rainer Keuchel]

It seems that gp register relative relocs
are not calculated correctly in pe-mips
when linking larger programs. The signed
REFLO sometimes point *before* program
start 0x11000. It looks like the calculation
is done as if REFLO were unsigned.
The calculation in ecoff-mips
looks better. Will try to fix this.

_startup:
   11000:	27bdfffc 	addiu	sp,sp,-4
   11004:	afbf0000 	sw	ra,0(sp)
   11008:	3c080001 	lui	t0,0x1
   1100c:	8d08b000 	lw	t0,-20480(t0) ! wrong
   11010:	00000000 	nop
   11014:	0100f809 	jalr	t0

_getstdfilex:
   1a0fc:	3c080001 	lui	t0,0x1
   1a100:	8d08f0b0 	lw	t0,-3920(t0) ! negative
   1a104:	01000008 	jr	t0
   1a108:	00000000 	nop