[libomptarget] Improve dlwrap compile time error diagnostic

[libomptarget] Improve dlwrap compile time error diagnostic

The dlwrap interface takes an explict arity, e.g. DLWRAP(cuAlloc, 2);
This probably can't be eliminated as it controls the argument list of an
external symbol, not an inline header function. If the arity given is too
big, the error from clang referring to the line is in the middle of
implementation details.

/usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/tuple:1277:7: error: static_assert failed
      due to requirement '0UL < tuple_size<std::tuple<>>::value' "tuple index is in range"
      static_assert(__i < tuple_size<tuple<>>::value,
      ^             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/tuple:1260:7: ...
/usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/tuple:1260:7: ...
/home/amd/llvm-project/openmp/libomptarget/include/dlwrap.h:93:27 ...

/home/amd/llvm-project/openmp/libomptarget/plugins/cuda/dynami...