When enabling the Vulkan validation layers, the 'validationLayerName'
variable technically went out of scope before vkCreateInstance() was
called. While most compilers won't clean up stack variables after random
'if' statements, some will, particularly when optimisation or memory
sanitizers are enabled.
This can lead to vkCreateInstance() segfaulting when
SDL_HINT_RENDER_VULKAN_DEBUG is enabled.
Instead, make the validationLayerName visible throughout the entire
VULKAN_CreateDeviceResources() function.
While we're at it, extract the validation layer name out into a
preprocessor #define, so that we are definitely using the same name in
VULKAN_ValidationLayersFound().
Signed-off-by: David Gow <david@ingeniumdigital.com>
b8a52c1237