Upgrade used QEMU to 4.2

[XVilka]

There were TONS of changes since:

• An upcoming https://wiki.qemu.org/ChangeLog/5.0
• https://wiki.qemu.org/ChangeLog/4.2
• https://wiki.qemu.org/ChangeLog/4.1
• https://wiki.qemu.org/ChangeLog/4.0
• https://wiki.qemu.org/ChangeLog/3.1
• https://wiki.qemu.org/ChangeLog/3.0
• https://wiki.qemu.org/ChangeLog/2.8
• https://wiki.qemu.org/ChangeLog/2.7
• https://wiki.qemu.org/ChangeLog/2.6
• https://wiki.qemu.org/ChangeLog/2.5
• https://wiki.qemu.org/ChangeLog/2.4
• https://wiki.qemu.org/ChangeLog/2.3

[aquynh]

Unicorn inspires many cool ideas, that we believe it deserves serious upgrade. This is what everyone wants, but unfortunately requires huge effort & lots of time.

Who can sponsor Unicorn 2? Contact us.

[Halastra]

Pardon the question, but I've just come across this fork of unicorn, which is claimed to follow upstream qemu more closely.

Are you familiar with this?
Do you think this fork might compromise this project's priorites (e.g. thread safeness, oss-fuzz compatibility, instrumentation etc.)?

[XVilka]

@aquynh I suggest to pin this issue.

[aquynh]

@XVilka yes