[HWASan] add assert about TagMaskByte

llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp

void HWAddressSanitizer::instrumentGlobals() {
   }
 
   MD5 Hasher;
   Hasher.update(M.getSourceFileName());
   MD5::MD5Result Hash;
   Hasher.final(Hash);
   uint8_t Tag = Hash[0];
 
+  // TagMaskByte must be one less than a power of two for the logic below to
+  // work reliably.
+  assert((TagMaskByte & (TagMaskByte + 1)) == 0);
   for (GlobalVariable *GV : Globals) {
     Tag &= TagMaskByte;
     // Skip tag 0 in order to avoid collisions with untagged memory.
     if (Tag == 0)
       Tag = 1;
     instrumentGlobal(GV, Tag++);
   }
 }