tests: Revive unixvictim binaries for Linux/x86*

They're useful for testing 32- and 64-bit builds on the same system.

tests/data/__init__.py

@@ -2,6 +2,7 @@
 
 import os
 import platform
+import sys
 
 
 system = platform.system()
@@ -9,6 +10,9 @@ if system == 'Windows':
     target_program = r"C:\Windows\notepad.exe"
 elif system == 'Darwin':
     target_program = os.path.join(os.path.dirname(__file__), "unixvictim-macos")
+elif system == 'Linux' and platform.machine() == 'x86_64':
+    arch = 'x86_64' if sys.maxsize > 2**32 else 'x86'
+    target_program = os.path.join(os.path.dirname(__file__), "unixvictim-" + system.lower() + "-" + arch)
 else:
     target_program = "/bin/cat"