DW_EH_PE_omit is FF so it cannot be a case
of encoding_lower8. Instead it can be a check against
the complete encoding.

updated to build with use_eflio in scons by default.  removed lots of std:: qualifiers that weren't needed

simplified interface to just return const pointers instead of shared ptrs.  no one needs ownership of anything

copied from security_transforms with git hash d508c94e31040d7bcafce6c8959fc6a8cc03a590, intentionally chosing to lose file history