RFC: Use nop instead of data16 on x86-64

[H. J. Lu]

elf64-x86-64.c uses data16 to remove instructions for TLS. For
example,

              /* LD->LE transition:
                 Ensure it is:
                 leaq foo@tlsld(%rip), %rdi; call __tls_get_addr@plt.
                 We change it into:
                 .word 0x6666; .byte 0x66; movl %fs:0, %rax.  */

I'd like to turn those data16 to proper single instuction nop. The
above will becomes

                 nopl 0(%rax); movl %fs:0, %rax

Any comments?


H.J.