set compiler flags for cross-platorm harmony

Author: ianfixes

lib/arduino_ci/cpp_library.rb

@@ -189,7 +189,7 @@ def build_for_test_with_configuration(test_file, aux_libraries, ci_gcc_config)
       base = File.basename(test_file)
       executable = File.expand_path("unittest_#{base}.bin")
       File.delete(executable) if File.exist?(executable)
-      args = ["-o", executable] + test_args(aux_libraries, ci_gcc_config) + [test_file]
+      args = ["-std=c++11", "-o", executable] + test_args(aux_libraries, ci_gcc_config) + [test_file]
       return nil unless run_gcc(*args)
       artifacts << executable
       executable