std::abort causes error when compiling CUDA with Clang in device code

[invexed]

Compiling with Clang 9 in CUDA mode results in the following compilation errors during its device code pass:

.../fmt-master/include/fmt/format-inl.h:50:8: error: expected identifier
  std::abort();
       ^
.../fmt-master/include/fmt/format-inl.h:50:3: error: unexpected namespace name 'std': expected expression
  std::abort();
  ^

One possible fix is to use std::terminate instead:

FMT_FUNC void assert_fail(const char* file, int line, const char* message) {
  print(stderr, "{}:{}: assertion failed: {}", file, line, message);
#if defined(__clang__) && defined(__CUDA__) && defined(__CUDA_ARCH__)
  std::terminate();
#else
  std::abort();
#endif
}

[vitaut]

{fmt} generally requires a C++ compiler but I'm open to a PR to workaround this issue in CUDA.