Compiler warnings

[otbrown]

Many warnings of the form

/home/otbrown/quantum/quest/source/QuEST/quest/src/core/accelerator.cpp: In function ‘qindex accel_statevec_packAmpsIntoBuffer(Qureg, ConstList64, ConstList64)’:
/home/otbrown/quantum/quest/source/QuEST/quest/src/core/accelerator.cpp:83:27: warning: unnecessary parentheses in declaration of ‘_ARRAY_gpu_statevec_packAmpsIntoBuffer’ [-Wparentheses]
   83 |     static constexpr auto (_ARRAY_##funcname) = GET_ONE_PARAM_TEMPLATED_FUNC_ARRAY( funcname ); \
      |                           ^~~~~~~~~~~~~~~~~~~
/home/otbrown/quantum/quest/source/QuEST/quest/src/core/accelerator.cpp:87:5: note: in expansion of macro ‘GET_FUNC_OPTIMISED_FOR_ONE_PARAM’
   87 |     GET_FUNC_OPTIMISED_FOR_ONE_PARAM( _GPU_FUNC, gpu_##funcsuffix, param ) \
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/otbrown/quantum/quest/source/QuEST/quest/src/core/accelerator.cpp:234:5: note: in expansion of macro ‘GET_CPU_OR_GPU_FUNC_OPTIMISED_FOR_ONE_PARAM’
  234 |     GET_CPU_OR_GPU_FUNC_OPTIMISED_FOR_ONE_PARAM( func, statevec_packAmpsIntoBuffer, qureg, qubits.size() );
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/otbrown/quantum/quest/source/QuEST/quest/src/core/accelerator.cpp:83:27: note: remove parentheses
   83 |     static constexpr auto (_ARRAY_##funcname) = GET_ONE_PARAM_TEMPLATED_FUNC_ARRAY( funcname ); \
      |                           ^~~~~~~~~~~~~~~~~~~
/home/otbrown/quantum/quest/source/QuEST/quest/src/core/accelerator.cpp:87:5: note: in expansion of macro ‘GET_FUNC_OPTIMISED_FOR_ONE_PARAM’
   87 |     GET_FUNC_OPTIMISED_FOR_ONE_PARAM( _GPU_FUNC, gpu_##funcsuffix, param ) \
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/otbrown/quantum/quest/source/QuEST/quest/src/core/accelerator.cpp:234:5: note: in expansion of macro ‘GET_CPU_OR_GPU_FUNC_OPTIMISED_FOR_ONE_PARAM’
  234 |     GET_CPU_OR_GPU_FUNC_OPTIMISED_FOR_ONE_PARAM( func, statevec_packAmpsIntoBuffer, qureg, qubits.size() );
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

in devel at the moment. Looks like a trivial fix, but I'll deal with it once I've finished merging #722 and #736.