Fix compilation warnings

Fix compilation warnings in ROOT6 build coming from compilation of dictionaries.  All the warnings are from the same header:
CondFormats/Serialization/interface/eos/portable_oarchive.hpp:324:15: warning: shift count >= width of type [-Wshift-count-overflow]
The warnings are fixed by special casing calculating the size of single byte types. Single byte types cause the warning because the shift count of 8 is >= 8(the size of the type in bits).