[lld] [lld][ELF] Fix a corner case of elf::getLoongArchPageDelta (PR #71907)

[via llvm-commits]

heiher wrote:

> > Another corner case?
> > DEST: 0 PC: 0x80000ffc
> > ```
> > 80000ffc: 05 00 00 1b  	pcalau12i	$a1, -524288
> > 80001000: 04 00 c0 02  	addi.d	$a0, $zero, 0
> > 80001004: e4 ff ff 17  	lu32i.d	$a0, -1
> > 80001008: 84 fc 3f 03  	lu52i.d	$a0, $a0, -1
> > 8000100c: 84 94 10 00  	add.d	$a0, $a0, $a1
> > ```
> > 
> > 
> >     
> >       
> >     
> > 
> >       
> >     
> > 
> >     
> >   
> > ugly test: https://gist.github.com/heiher/3c7a2a9e7d05354e818b50d69e40b8cb
> 
> ld is correct in this case.
> 
> ```
>     80000ffc:   1b000004        pcalau12i       $a0, -524288(0x80000)
>     80001000:   02c00001        addi.d          $ra, $zero, 0
>     80001004:   16000001        lu32i.d         $ra, 0
>     80001008:   03000021        lu52i.d         $ra, $ra, 0
>     8000100c:   00109021        add.d           $ra, $ra, $a0
> ```
> 
> @MQ-mengqing Can you post an example you mentioned in [rui314/mold#1131 (comment)](https://github.com/rui314/mold/issues/1131#issuecomment-1771892552) ?

I found that different ld versions have different results, it doesn't seem to be completely correct? :disappointed: 

### DEST: 0 PC: 0x80000ffc

#### ld 2.40 (correct)

```asm
    80000ffc:	1b000005 	pcalau12i   	$a1, -524288(0x80000)
    80001000:	02c00004 	addi.d      	$a0, $zero, 0
    80001004:	16000004 	lu32i.d     	$a0, 0
    80001008:	03000084 	lu52i.d     	$a0, $a0, 0
    8000100c:	00109484 	add.d       	$a0, $a0, $a1 # $a0 = 0
```

#### ld 2.41 or git mainline (incorrect)

```asm
    80000ffc:	1b000005 	pcalau12i   	$a1, -524288(0x80000)
    80001000:	02c00004 	addi.d      	$a0, $zero, 0
    80001004:	17ffffe4 	lu32i.d     	$a0, -1(0xfffff)
    80001008:	033ffc84 	lu52i.d     	$a0, $a0, -1(0xfff)
    8000100c:	00109484 	add.d       	$a0, $a0, $a1 # $a0 = 0xffffffff00000000
```

### DEST: 0 PC: 0x80001000

#### ld 2.40 (incorrect)

```asm
    80001000:	1affffe5 	pcalau12i   	$a1, 524287(0x7ffff)
    80001004:	02c00004 	addi.d      	$a0, $zero, 0
    80001008:	16000004 	lu32i.d     	$a0, 0
    8000100c:	03000084 	lu52i.d     	$a0, $a0, 0
    80001010:	00109484 	add.d       	$a0, $a0, $a1 # $a0 = 0x100000000
```

#### ld 2.41 or git mainline (correct)

```asm
    80001000:	1affffe5 	pcalau12i   	$a1, 524287(0x7ffff)
    80001004:	02c00004 	addi.d      	$a0, $zero, 0
    80001008:	17ffffe4 	lu32i.d     	$a0, -1(0xfffff)
    8000100c:	033ffc84 	lu52i.d     	$a0, $a0, -1(0xfff)
    80001010:	00109484 	add.d       	$a0, $a0, $a1 # $a0 = 0
```


https://github.com/llvm/llvm-project/pull/71907