[libcpu] Fix CPUID register overwriting bug

Well god damnit, when i converted the `cpu::cpu_id::regs` struct to a
union, i was super sloppy and forgot to wrap the existing fields in
their own anonymous struct. I have been wrong about CPUID vales for
ages.

src/libraries/cpu/cpu/cpu_id.h

@@ -27,8 +27,10 @@ public:
     struct regs {
         union {
             uint32_t reg[4];
+            struct {
                 uint32_t eax, ebx, ecx, edx;
             };
+        };
 
         /// Return true if bit |bit| of EAX is set
         bool eax_bit(unsigned bit) { return (eax >> bit) & 0x1; }