Fix cpu architecture detection on x86 during cmake configuration

[serge-sans-paille]

Summary

In presence of unknown models, the program could return 0 without output, which is unexpected. Return unknown as expected in that case.

[itaraban]

LGTM

[serge-sans-paille]

Commited as 1cdde847bb01c4b1e490d8e902ac99096df75fd4, don't know why phabricator doesn't auto-close it.

[serge-sans-paille]

and thanks @itaraban for the review, of course.

cmake/modules/DetectX86CPUArchitecture.c

case 6:
         printf("merom");
         break;
       case 28:
         printf("atom");
         break;
       case 14:
         printf("core");
         break;
+      default:
+        printf("unknown");
+        return 1;
       }
       break;
     case 7:
       printf("itanium");
       break;
     default:
       printf("unknown");
       return 1;