There is some behavior of GCC compilers before GCC 9.0 that is incompatible with the specification of OpenMP 4.0. The workaround was using the workaround any time a GCC compiler >= 9.0 was used. The proper behavior is to only use the workaround when the GCC compiler is being used and the version of the compiler is less than 9.0.
Also, switch to using VTKM_GCC to check for the GCC compiler instead of GNUC. The problem with using GNUC is that many other compilers pretend to be GCC by defining this macro, but in cases like compiler workarounds it is not accurate.