Consolidate compiler (version) detection

[bernhardmgruber]

We have a couple of headers detecting what kind of compiler is in use and exposing macros accordingly:

libcu++ seems to be at root, detecting what compiler is in use in: cuda/std/__cccl/compiler.h and defines macros like _CCCL_COMPILER_GCC. However, no version macros are exposed.

Thrust has thrust/detail/config/compiler.h, which uses the libcu++ macros and replicates the information by defining THRUST_HOST_COMPILER to a set of predefined constants, e.g. THRUST_HOST_COMPILER_GCC (which is 2). Thrust additionally defines compiler version macros like THRUST_GCC_VERSION.

CUB basically duplicates what Thrust does, exposing macros like CUB_HOST_COMPILER or CUB_GCC_VERSION.

I would really like all these macros to be consolidated into a single header inside libcu++, so I have a consistent way of asking what compiler at which version is in use.

[miscco]

the issue here is that the THRUST_* and CUB_* macros are user facing and cannot be removed as is.

I tried to remove all occurrences of those but I see that we missed some internally.

[bernhardmgruber]

I would at least like to have compiler version macros in libcu++, so I could consistenly use the libcu++ macros across Thrust, CUB and libcu++. This would also allow us to deprecate and remove the Thrust and CUB macros at some point.