Fix assembly to only test the valid 8 bits of register EAX

Currently we test all 32 bits, but the upper 24 bits could be garbage
depending on what the compiler does. If any of those bits are set
we'll think we're in replay when we're really recording.

Author: rocallahan

src/preload/syscallbuf.c

@@ -1598,7 +1598,7 @@ static void memcpy_input_parameter(void* buf, void* src, int size) {
  */
 static void rdtsc_recording_only(uint32_t buf[2]) {
   unsigned char tmp_in_replay = *rr_page_replay_flag_addr();
-  __asm__ __volatile__("test %%eax,%%eax\n\t"
+  __asm__ __volatile__("test %%al,%%al\n\t"
                        "jne 1f\n\t"
                        "rdtsc\n\t"
                        "mov %%eax,(%1)\n\t"