[llvm] [JITLink][LoongArch] Ignore R_LARCH_RELAX and check R_LARCH_ALIGN (PR #121097)

[via llvm-commits]

zhaoqi5 wrote:

`R_LARCH_ALIGN` cannot be simply ignored. Although tests of `clang-repl` do not meet with error.
But error may occur. For example:
```
    .text
    .globl main
    .type main, at function
main:
    nop 
    ret 

    .globl br16
br16:

test_br16:
    .p2align 4
    la.pcrel $a0, br16
    .skip (1 << 17 - 16) 
    beq $t1, $t2, %b16(br16)
```
- Without relax: `llvm-mc --triple=loongarch64 --filetype=obj  t.s -o - | llvm-objdump -d -`, two nops should be inserted.
```
0000000000000000 <main>:
       0: 00 00 40 03  	nop
       4: 20 00 00 4c  	ret

0000000000000008 <test_br16>:
       8: 00 00 40 03  	nop
       c: 00 00 40 03  	nop
      10: 04 00 00 1a  	pcalau12i	$a0, 0
      14: 84 00 c0 02  	addi.d	$a0, $a0, 0
		...
   20008: ae 01 00 58  	beq	$t1, $t2, 0 <test_br16+0x20000>
```
- But with relax: `llvm-mc --triple=loongarch64 --filetype=obj -mattr=+relax t.s -o - | llvm-objdump -d -`, three nops are inserted. The linker is expected to remove one nop to align pcalau12i.
```
0000000000000000 <main>:
       0: 00 00 40 03  	nop
       4: 20 00 00 4c  	ret

0000000000000008 <test_br16>:
       8: 00 00 40 03  	nop
       c: 00 00 40 03  	nop
      10: 00 00 40 03  	nop
      14: 04 00 00 1a  	pcalau12i	$a0, 0
      18: 84 00 c0 02  	addi.d	$a0, $a0, 0
		...
   2000c: ae 01 00 58  	beq	$t1, $t2, 0 <test_br16+0x20004>
```
If we ignore `R_LARCH_ALIGN` in jitlink. Nops will not be removed and `beq` will be out of range while running `llvm-jitlink t.o`.
```
llvm-jitlink error: In graph t.o, section .text: relocation target "br16" at address 0x7fffa4000008 is out of range of Branch16PCRel fixup at 0x7fffa402000c (main, 0x7fffa4000000 + 0x2000c)
```

https://github.com/llvm/llvm-project/pull/121097