Test cross-ISA emulated calls

[andreiw]

Validate that one emulated binary (e.g. x64 app) can call an interface provided by another emulated binary with a different ISA (e.g. AArch64 driver).

This is primarily test application / test driver work + a fixes to Emulator.c/Cpu.c. Namely, it needs to treat code with ImageRecords having a different arch as being native.