build: Do not overwrite CMAKE_ASM-ATT_FLAGS
build: Do not overwrite CMAKE_ASM-ATT_FLAGS

Allows passing flags to assembler in order to build 32-bit targets
on 64-bit platforms.

A 32-bit build can be produced by passing -DCMAKE_ASM-ATT_FLAGS=--32
to cmake.

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