[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/dynamic_cuda/cuda.cpp:34:1: note: in
      instantiation of template class 'dlwrap::trait<cudaError_enum (*)(unsigned long *, unsigned
      long)>::arg<2>' requested here
DLWRAP(cuMemAlloc, 3);
^
/home/amd/llvm-project/openmp/libomptarget/include/dlwrap.h:51:31: ...
/home/amd/llvm-project/openmp/libomptarget/include/dlwrap.h:166:3: ...
/home/amd/llvm-project/openmp/libomptarget/include/dlwrap.h:133:3: ...
/home/amd/llvm-project/openmp/libomptarget/include/dlwrap.h:186:37: ...

If the arity is too small, the diagnostic is better:

cuda/dynamic_cuda/cuda.cpp:34:1: error: too few
      arguments to function call, expected 2, have 1
DLWRAP(cuMemAlloc, 1);

This patch changes the diagnostic to:

cuda/dynamic_cuda/cuda.cpp:34:1: error:
      static_assert failed due to requirement '1 == trait<cudaError_enum (*)(unsigned long *, unsigned
      long)>::nargs' "Arity Error"
DLWRAP(cuMemAlloc, 1);

or

cuda/dynamic_cuda/cuda.cpp:34:1: error:
      static_assert failed due to requirement '3 == trait<cudaError_enum (*)(unsigned long *, unsigned
      long)>::nargs' "Arity Error"
DLWRAP(cuMemAlloc, 3);

Reviewed By: tianshilei1992

Differential Revision: https://reviews.llvm.org/D102858