[Click] click_get_cycles() on x86_64

[Salman Abdul Baset]

In function click_get_cycles() defined in include/click/glue.hh, there is 
no #ifdef for x86_64. Consequently, on the machine I am testing (quad 
core, x86_64) click_get_cycles() returns zero.

I copied the code from
#if CLICK_LINUXMODULE && HAVE_INT64_TYPES && __i386__
to fix it:

<code>
#elif CLICK_LINUXMODULE && HAVE_INT64_TYPES && __x86_64__
     uint64_t x;
     __asm__ __volatile__ ("rdtsc" : "=A" (x));
     return x;
</code>

Is this a correct way to do this?

Thanks
Salman