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* openmp_wrapper.h stubs signature use __GOMP_NOTHROW

Fix #3915. OpenMP stubs do not use the noexcept attibute which is present in the gcc version of openmp, and which trigger compilation errors as seen below. dmlc-core uses the same technique and macro.

/usr/lib/gcc/x86_64-linux-gnu/9/include/omp.h:114:12: error: declaration of ‘int omp_get_thread_num() noexcept’ has a different exception specifier
  114 | extern int omp_get_thread_num (void) __GOMP_NOTHROW;
      |            ^~~~~~~~~~~~~~~~~~
...
xxx/include/LightGBM/utils/openmp_wrapper.h:81:14: note: from previous declaration ‘int omp_get_thread_num()’
   81 |   inline int omp_get_thread_num() {return 0;}
      |              ^~~~~~~~~~~~~~~~~~

* move __GOMP_NOTHROW definition in the no open mp stub conditional branch

* Update include/LightGBM/utils/openmp_wrapper.h

Yes make sense, just changed it
Co-authored-by: James Lamb <jaylamb20@gmail.com>

* add NOLINT macro to disable cpplint on a safe line of code
Co-authored-by: James Lamb <jaylamb20@gmail.com>