[libomptarget][nfc] Improve static assert message in dlwrap

[JonChesterfield]

Summary

Revision of D102858. Raise dlwrap arity argument to template argument
so the correct value is given in the error message. E.g. '2 == 1' instead of
'2 == trait<>::nargs'.

Arity higher than it should be:
Before diff

$/plugins/cuda/dynamic_cuda/cuda.cpp:23:1: error: 
      static_assert failed due to requirement '2 == trait<cudaError_enum (*)(unsigned int)>::nargs'
      "Arity Error"
DLWRAP_INTERNAL(cuInit, 2);
^~~~~~~~~~~~~~~~~~~~~~~~~~
...
$/include/dlwrap.h:166:3: note: expanded from macro
      'DLWRAP_COMMON'
  static_assert(ARITY == trait<decltype(&SYMBOL)>::nargs, "Arity Error");      \

After diff
In file included from $/plugins/cuda/dynamic_cuda/cuda.cpp:16:

$/include/dlwrap.h:131:3: error: static_assert failed due to
      requirement '2UL == 1UL' "Arity Error"
  static_assert(Requested == Required, "Arity Error");
  ^             ~~~~~~~~~~~~~~~~~~~~~
$/plugins/cuda/dynamic_cuda/cuda.cpp:23:1: note: in
      instantiation of function template specialization 'dlwrap::verboseAssert<2UL, 1UL>' requested
      here
DLWRAP_INTERNAL(cuInit, 2);

Arity lower than it should be:
Before diff

$/plugins/cuda/dynamic_cuda/cuda.cpp:131:10: error: no
      matching function for call to 'dlwrap_cuInit'
  return dlwrap_cuInit(X);
         ^~~~~~~~~~~~~
$/plugins/cuda/dynamic_cuda/cuda.cpp:23:1: note: candidate
      function not viable: requires 0 arguments, but 1 was provided
DLWRAP_INTERNAL(cuInit, 0);

After diff
In file included from $/plugins/cuda/dynamic_cuda/cuda.cpp:16:

$/include/dlwrap.h:131:3: error: static_assert failed due to
      requirement '0UL == 1UL' "Arity Error"
  static_assert(Requested == Required, "Arity Error");
  ^             ~~~~~~~~~~~~~~~~~~~~~
$/plugins/cuda/dynamic_cuda/cuda.cpp:23:1: note: in
      instantiation of function template specialization 'dlwrap::verboseAssert<0UL, 1UL>' requested
      here
DLWRAP_INTERNAL(cuInit, 0);

[jdoerfert]

LG

openmp/libomptarget/include/dlwrap.h

 } // namespace type
 
 template <size_t N, size_t... Is>
 constexpr std::array<const char *, N> static getSymbolArray(
     std::index_sequence<Is...>) {
   return {{dlwrap::type::symbol<Is>::call()...}};
 }
 
+template <size_t Requested, size_t Required> constexpr void verboseAssert() {
+  static_assert(Requested == Required, "Arity Error");
+}
+
 } // namespace dlwrap
 
 #define DLWRAP_INSTANTIATE(SYM_USE, SYM_DEF, ARITY)                            \
   DLWRAP_INSTANTIATE_##ARITY(SYM_USE, SYM_DEF,                                 \
                              dlwrap::trait<decltype(&SYM_USE)>)
 
 #define DLWRAP_FINALIZE_IMPL()                                                 \
   static size_t dlwrap::size() { return DLWRAP_ID(); }                         \

 
 #define DLWRAP_COMMON(SYMBOL, ARITY)                                           \
   DLWRAP_INC();                                                                \
   DLWRAP_SYMBOL(SYMBOL, DLWRAP_ID() - 1);                                      \
   namespace dlwrap {                                                           \
   struct SYMBOL##_Trait : public dlwrap::trait<decltype(&SYMBOL)> {            \
     using T = dlwrap::trait<decltype(&SYMBOL)>;                                \
     static T::FunctionType get() {                                             \
+      verboseAssert<ARITY, trait<decltype(&SYMBOL)>::nargs>();                 \
       constexpr size_t Index = DLWRAP_ID() - 1;                                \
       void *P = *dlwrap::pointer(Index);                                       \
       return reinterpret_cast<T::FunctionType>(P);                             \
     }                                                                          \
   };                                                                           \
-  static_assert(ARITY == trait<decltype(&SYMBOL)>::nargs, "Arity Error");      \
   }
 
 #define DLWRAP_IMPL(SYMBOL, ARITY)                                             \
   DLWRAP_COMMON(SYMBOL, ARITY);                                                \
   DLWRAP_INSTANTIATE(SYMBOL, SYMBOL, ARITY)
 
 #define DLWRAP_INTERNAL_IMPL(SYMBOL, ARITY)                                    \
   DLWRAP_COMMON(SYMBOL, ARITY);                                                \