tests: make it work aka hide HUDElements

Currently the test is pulling an external reference to HUDElements,
which is unresolved so the test fails to link.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>

meson.build

@@ -271,6 +271,7 @@ if get_option('tests').enabled()
       'src/mesa/util/os_time.c',
       'src/file_utils.cpp',
     ),
+    cpp_args: ['-DTEST_ONLY'],
     dependencies: [
       cmocka_dep,
       spdlog_dep,

src/amdgpu.cpp

@@ -156,9 +156,11 @@ void amdgpu_metrics_polling_thread() {
 	memset(metrics_buffer, 0, sizeof(metrics_buffer));
 
 	while (1) {
+#ifndef TEST_ONLY
 		if (HUDElements.params->no_display && !logger->is_active())
 			usleep(100000);
 		else
+#endif
 			amdgpu_get_samples_and_copy(metrics_buffer, gpu_load_needs_dividing);
 	}
 }