stdtype: only provide specializations of GetType for stdint-based types
stdtype: only provide specializations of GetType for stdint-based types

This wll hopefully fix uint64_t sometimes being mappd to "unsigned long"
and sometimes "unsigned long long" as the type string.

ornladios/ADIOS2,JasonRuonanWang/ADIOS2,ornladios/ADIOS2,ornladios/ADIOS2,JasonRuonanWang/ADIOS2,JasonRuonanWang/ADIOS2,JasonRuonanWang/ADIOS2,JasonRuonanWang/ADIOS2,ornladios/ADIOS2,ornladios/ADIOS2