Adds architecture tags to raw traces, propagated to final traces in a new marker type. Adds reader support for the new type.
Adds a check for unhandled architectures to raw2trace.
Adds checks for unhandled architectures to the opcode_mix and view tools. To reach that point, relaxes the ELF header checks to allow libraries of the same bitwidth but different architectures (i#1345 prevents allowing all libraries), so we can map in the other-arch libraries.
Updates the existing aarch64 raw trace files to contain architecture tags, and updates the x86 failure message.
Cross-architecture handling of these same files was tested manually with a prototype which will be committed in the future.