extend "x86_mode" to support multiple modes

From bruen...@google.com on October 08, 2014 00:04:22

Even if for ARM there is no mixed-mode in user-mode and we wouldn't care about it in regular DR unless we do whole-OS, for drdecodelib we do want to support multiple modes, or possibly for a tool who wants to go decode a file.

The proposal is to deprecate {get,set}_x86_mode() and replace them with {get,set}_isa_mode(dcontext, enum) where the enum can be extended for each mode: IA-32 vs AMD64, ARM vs Thumb, etc.

We'll move set_x86_mode will be moved to core/arch/x86/decode_private.h and swap all internal uses to the new routine as well.

Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1550