tests: Suppress gtest warnings
tests: Suppress gtest warnings

Gtest generates GCC warnings for some signed/unsigned mismatches.
Suppress this for the test output.

Change-Id: Ifa3406610e980b81e091976a062cde6457a71377

KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers