Add Multiple Exit Support for More Architectures

[domenukk]

Right now, multiple exits are only supported on X64 (X86_64).
The way it works on X64 is as follows:

• When mapping a page, a syscall insn is patched in for each exit in this page
• When a syscall hook is triggered (cheap), the hook checks if it belongs to an exit
• Exit.

The other archs will need an alternative to syscall which is cheap in unicorn.
For X86, UB2 might be an option.
Any illegal instruction could maybe be used.

[domenukk]

Instead of building some awkward wrapper around Unicorn, I patched multiple exits in in this uc branch.
domenukk/unicornafl@81802f5
Cleaning this up now, then merging it to AFL++, then including it here.
Soon(tm)

[domenukk]

Merged to master with commit 3ac3007