message: c-bindings: do the EXPECT_EQ using std::string
  For better error messages if the tests fail...
diff: @@ -368,11 +368,11 @@ TEST(ADIOS2_C_API, ReturnedStrings)
  adios2_remove_all_ios(adiosH);
  - EXPECT_EQ(strcmp(engine_type, "BP3"), 0);
  - EXPECT_EQ(strcmp(var_name, "varI8"), 0);
  - EXPECT_EQ(strcmp(attr_name, "intAttr"), 0);
  + EXPECT_EQ(std::string(engine_type), "BP3");
  + EXPECT_EQ(std::string(var_name), "varI8");
  + EXPECT_EQ(std::string(attr_name), "intAttr");
  #ifdef ADIOS2_HAVE_BZIP2
  - EXPECT_EQ(strcmp(op_type, "bzip2"), 0);
  + EXPECT_EQ(std::string(op_type), "bzip2");
  #endif
  }
  }
  