[compiler-rt] Fix a warning

This patch fixes:

  compiler-rt/lib/builtins/cpu_model.c:590:5: error: unannotated
  fall-through between switch labels [-Werror,-Wimplicit-fallthrough]

by adding a missing "break;".

Author: kazutakahirata

compiler-rt/lib/builtins/cpu_model.c

@@ -586,6 +586,7 @@ getIntelProcessorTypeAndSubtype(unsigned Family, unsigned Model,
       CPU = "clearwaterforest";
       *Type = INTEL_COREI7;
       *Subtype = INTEL_CLEARWATERFOREST;
+      break;
 
     case 0x57:
       CPU = "knl";