common: Get rid of EBX restoration for x86-64.

It is not a PIC register, break out x86-specific PIC support.
This would break x86-64 for less forgiving assemblers that
(correctly) do not accept pushl/popl.

regressions/common.h

@@ -367,7 +367,7 @@ aff_iterate_core(struct affinity *acb CK_CC_UNUSED, unsigned int *core)
 CK_CC_INLINE static uint64_t
 rdtsc(void)
 {
-#if defined(__x86_64__) || defined(__x86__)
+#if defined(__x86_64__)
 	uint32_t eax = 0, edx;
 #if defined(CK_MD_RDTSCP)
 	__asm__ __volatile__("rdtscp"
@@ -377,7 +377,30 @@ rdtsc(void)
 
 	return (((uint64_t)edx << 32) | eax);
 #else
+        __asm__ __volatile__("cpuid;"
+                             "rdtsc;"
+                                : "+a" (eax), "=d" (edx)
+                                :
+                                : "%ebx", "%ecx", "memory");
+
+        __asm__ __volatile__("xorl %%eax, %%eax;"
+                             "cpuid;"
+                                :
+                                :
+                                : "%eax", "%ebx", "%ecx", "%edx", "memory");
 
+        return (((uint64_t)edx << 32) | eax);
+#endif /* !CK_MD_RDTSCP */
+#elif defined(__x86__)
+	uint32_t eax = 0, edx;
+#if defined(CK_MD_RDTSCP)
+	__asm__ __volatile__("rdtscp"
+				: "+a" (eax), "=d" (edx)
+				:
+				: "%ecx", "memory");
+
+	return (((uint64_t)edx << 32) | eax);
+#else
         __asm__ __volatile__("pushl %%ebx;"
 			     "cpuid;"
                              "rdtsc;"