support 32-bit ELF in 64-bit drsyms (and possibly vice versa)

From bruen...@google.com on August 29, 2014 15:48:41

Xref issue #1345 for the core supporting mixed libraries.

drsyms, though, has a greater need for it, for offline tools that want to analyze a mixture (e.g., drcov analyzing several runs of different bitwidths but from the same sources).

Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1532