ArchCapstoneBuilder panics in qemu_user

[dlmarrero]

Describe the bug When building a fuzzer using ARM qem_user, the fuzzer panics at runtime with the following error:

thread main panicked at 'called `Result::unwrap()` on an `Err` value: CustomError("Must specify mode for arm::ArchCapstoneBuilder with `mode()` method")', /libafl/libafl_qemu/src/blocks.rs:46:53

The fix for my use case was to change blocks.rs:46 to be:

let mode = if pc & 1 == 1 {
    arch::arm::ArchMode::Thumb
} else {
    arch::arm::ArchMode::Arm
}

let cs = crate::capstone()
    .mode(arch::arm::ArchMode::Arm)
    .detail(true)
    .build()
    .unwrap();

Maybe it would be better to check the Thumb bit in Regs::Cpsr? Also not sure if this is a bug in LibAFL or Capstone since crate::capstone() returns arm::ArchCapstoneBuilder here.

[andreafioraldi]

https://github.com/AFLplusplus/LibAFL/pull/1136