gnu: Add unicorn-2.0.

This older version of unicorn is required by python-angr. Without
it, python-angr does not pass check [0]. angr upstream is aware of
the problem but does not yet support newer versions of unicorn [1].
Other distributions, like Nix, solve this by packaging the older
version of unicorn specifically for angr [2], let's do the same!

* gnu/packages/emulators.scm (unicorn-2.0): New variable.

[0]: https://issues.guix.gnu.org/78132
[1]: https://github.com/angr/angr/issues/4921
[2]: https://github.com/NixOS/nixpkgs/pull/388155

Signed-off-by: Hilton Chain <hako@ultrarare.space>

gnu/packages/emulators.scm

@@ -3862,6 +3862,18 @@ graphic filters.  Some of its features include:
 emulator framework based on QEMU.")
     (license license:gpl2+)))
 
+(define-public unicorn-2.0
+  (package
+    (inherit unicorn)
+    (name "unicorn")
+    (version "2.0.1.post1")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (pypi-uri name version))
+       (sha256
+        (base32 "0mlfs8qfi0clyncfkbxp6in0cpl747510i6bqymwid43xcirbikz"))))))
+
 (define-public ppsspp
   (package
     (name "ppsspp")