build: slightly change files to pass compilation

Compiled using Clang and encountered errors on ambiguous pointer
type, implicit conversion NULL to bool, and unused function, etc.
As a fix, this patch slightly updates the related codes.

Change-Id: I4a73d66293313dda36749036f5c73aaf2a445231

test/app/test.cpp

@@ -73,7 +73,7 @@ int main(int argc, char** argv) {
 
   TestHsa::HsaInstantiate();
 
-  std::thread t[thrs];
+  std::vector<std::thread> t(thrs);
   for (int n = 0; n < thrs; ++n) {
     t[n] = std::thread(thread_fun, kiter, diter, agents_number);
   }