the current cpuid logic clobbers %ebx.  this is OK if the code is not PIC, but 
if you're building PIEs, it'll fail because %ebx is the PIC register and gcc 
doesn't let you clobber it.

simple fix:
  int ax, bx, cx, dx;
  __asm__ __volatile__ (
      "mov %%ebx, %%edi;"
      "cpuid;"
      "mov %%ebx, %%esi;"
      "mov %%edi, %%ebx;"
      :"=a" (ax), "=S" (bx), "=c" (cx), "=d" (dx) : "a"(1) :"edi");

it's a few more insns on x86_64 or i386/non-pic, so if you want, you could do 
something like:
#if defined(STRESSAPPTEST_CPU_I686) && defined(__PIC__)
 ... do pic version here ...
#else
 ... do non-pic version here ...
#endif