[Test][JITLink] Save rbx in ExecutionEngine/JITLink/x86-64/ELF_vtune.s (#86472)

The callee should preserve rbx according to the calling convention, but
it is not in the test case `ExecutionEngine/JITLink/x86-64/ELF_vtune.s`.
Not preserving the rbx register may result in some random error to the
caller function. This patch adds the missing command to preserve the
rbx.

Author: yingcong-wu

llvm/test/ExecutionEngine/JITLink/x86-64/ELF_vtune.s

@@ -20,12 +20,14 @@ main:
         .cfi_def_cfa_offset 16
         .cfi_offset 6, -16
         movq    %rsp, %rbp
+        pushq   %rbx
         .cfi_def_cfa_register 6
-        movl    %edi, -4(%rbp)
-        movq    %rsi, -16(%rbp)
-        movl    -4(%rbp), %ebx
+        movl    %edi, -16(%rbp)
+        movq    %rsi, -24(%rbp)
+        movl    -16(%rbp), %ebx
         addl    $1, %ebx
-	movl   $0, %eax
+        movl    $0, %eax
+        popq    %rbx
         popq    %rbp
         .cfi_def_cfa 7, 8
         ret