Unexpected augmentation character: B

[jschwe]

The LLVM libunwind parser also defines B and Gaugmentation strings on aarch64, see:
https://github.com/llvm/llvm-project/blob/main/libunwind/src/DwarfParser.hpp#L433-L436

This causes bloaty to crash, since it doesn't expect these characters:

bloaty/src/eh_frame.cc

Line 194 in c8e8bc6

THROW("Unexepcted augmentation character");