mips: use preferred asm mnemomic jr for better assembler compatibility

The LLVM assembler reportedly assembles the form using the j mnemonic
incorrectly (see issue 107460). The jr form is canonical and avoids
this problem, so use it instead.

crt/mips/crtn.s

@@ -3,11 +3,11 @@
 .section .init
 	lw $gp,24($sp)
 	lw $ra,28($sp)
-	j $ra
+	jr $ra
 	addu $sp,$sp,32
 
 .section .fini
 	lw $gp,24($sp)
 	lw $ra,28($sp)
-	j $ra
+	jr $ra
 	addu $sp,$sp,32

crt/mips64/crtn.s

@@ -3,11 +3,11 @@
 .section .init
 	ld $gp,16($sp)
 	ld $ra,24($sp)
-	j $ra
+	jr $ra
 	daddu $sp,$sp,32
 
 .section .fini
 	ld $gp,16($sp)
 	ld $ra,24($sp)
-	j $ra
+	jr $ra
 	daddu $sp,$sp,32

crt/mipsn32/crtn.s

@@ -2,11 +2,11 @@
 .section	.init
 	ld	$gp, 16($sp)
 	ld	$ra, 24($sp)
-	j	$ra
+	jr	$ra
 	addu	$sp, $sp, 32
 
 .section	.fini
 	ld	$gp, 16($sp)
 	ld	$ra, 24($sp)
-	j	$ra
+	jr	$ra
 	addu	$sp, $sp, 32