Build broken after removal of _CCCL_NODISCARD in #4265

[oleksandr-pavlyk]

After rebasing development branch on top of recent main, the build of cccl.c.parallel started failing:

 [14/19] Building CUDA object _parent_cccl/c/parallel/CMakeFiles/cccl.c.parallel.dir/src/transform.cu.o
  FAILED: _parent_cccl/c/parallel/CMakeFiles/cccl.c.parallel.dir/src/transform.cu.o
  /usr/bin/sccache /usr/local/cuda/bin/nvcc -forward-unknown-to-host-compiler -ccbin=/usr/bin/g++ -DCCCL_C_EXPERIMENTAL=1 -DNVRTC_GET_TYPE_NAME=1 -D_CCCL_NO_SYSTEM_HEADER -D_CUB_HAS_TRANSFORM_UBLKCP=0 -Dcccl_c_parallel_EXPORTS -I/home/coder/cccl/c/parallel/include -I/home/coder/cccl/c/parallel/src -I/home/coder/cccl/lib/cmake/cub/../../../cub -I/home/coder/cccl/lib/cmake/libcudacxx/../../../libcudacxx/include -I/home/coder/cccl/lib/cmake/thrust/../../../thrust -isystem /usr/local/cuda/targets/x86_64-linux/include -O3 -DNDEBUG -std=c++20 "--generate-code=arch=compute_52,code=[compute_52,sm_52]" -Xcompiler=-fPIC --extended-lambda -Xcudafe=--display_error_number -Wno-deprecated-gpu-targets -Xcudafe=--promote_warnings -Wreorder -Xcompiler=-Werror -Xcompiler=-Wall -Xcompiler=-Wextra -Xcompiler=-Wreorder -Xcompiler=-Winit-self -Xcompiler=-Woverloaded-virtual -Xcompiler=-Wcast-qual -Xcompiler=-Wpointer-arith -Xcompiler=-Wvla -Xcompiler=-Wno-gnu-line-marker -Xcompiler=-Wno-gnu-zero-variadic-macro-arguments -Xcompiler=-Wno-unused-function -Xcompiler=-Wno-noexcept-type -MD -MT _parent_cccl/c/parallel/CMakeFiles/cccl.c.parallel.dir/src/transform.cu.o -MF _parent_cccl/c/parallel/CMakeFiles/cccl.c.parallel.dir/src/transform.cu.o.d -x cu -c /home/coder/cccl/c/parallel/src/transform.cu -o _parent_cccl/c/parallel/CMakeFiles/cccl.c.parallel.dir/src/transform.cu.o
  /home/coder/cccl/lib/cmake/libcudacxx/../../../libcudacxx/include/cuda/std/__floating_point/arithmetic.h(31): error: this declaration has no storage class or type specifier
    _CCCL_NODISCARD
    ^

  /home/coder/cccl/lib/cmake/libcudacxx/../../../libcudacxx/include/cuda/std/__floating_point/arithmetic.h(31): error: expected a ";"
                   __attribute__((__visibility__("hidden"))) inline __attribute__((host)) __attribute__((device))
                                                             ^

  /home/coder/cccl/lib/cmake/libcudacxx/../../../libcudacxx/include/cuda/std/__floating_point/arithmetic.h(44): error #12-D: parsing restarts here after previous syntax error
    } } }
    ^

  Remark: The warnings can be suppressed with "-diag-suppress <warning-number>"

  /home/coder/cccl/lib/cmake/libcudacxx/../../../libcudacxx/include/cuda/std/__floating_point/cccl_fp.h(107): error: this declaration has no storage class or type specifier
    _CCCL_NODISCARD
    ^

  /home/coder/cccl/lib/cmake/libcudacxx/../../../libcudacxx/include/cuda/std/__floating_point/cccl_fp.h(106): error: declaration is incompatible with template parameter "_Tp" (declared at line 30 of /home/coder/cccl/lib/cmake/libcudacxx/../../../libcudacxx/include/cuda/std/__floating_point/arithmetic.h)
    template <__fp_format _Fmt>
                          ^

  /home/coder/cccl/lib/cmake/libcudacxx/../../../libcudacxx/include/cuda/std/__floating_point/cccl_fp.h(107): error: expected a ";"
                   __attribute__((__visibility__("hidden"))) inline __attribute__((host)) __attribute__((device))
                                                             ^

  /home/coder/cccl/lib/cmake/libcudacxx/../../../libcudacxx/include/cuda/std/__floating_point/cccl_fp.h(119): error #12-D: parsing restarts here after previous syntax error
    } } }
    ^

  7 errors detected in the compilation of "/home/coder/cccl/c/parallel/src/transform.cu".

The reason is that definition for _CCCL_NODISCARD macro had been removed in #4265 , but few instances of its use escaped replacing.