(NATIVECPU) added #define for device binary target

[uwedolinsky]

Added missing #define UR_DEVICE_BINARY_TARGET_NATIVE_CPU. We need this to name the binary type for the DPC++ NativeCPU target.

[pbalcer]

Thank you for your contribution. The header files containing the unified runtime specification are generated automatically, so they must not be modified manually, as this patch proposes. See the contribution guide for more information.

[kbenzie]

As @pbalcer says these files are generated from the yaml description, this macro should be added here followed by building the generate target @uwedolinsky.

[uwedolinsky]

Thanks @pbalcer and @kbenzie for the comments which (I think) are addressed now. Please could you review? Thank you!