Remove old interpreter input when running tests (#864)

This PR makes a small change to the `lit` lines we use to run checks on
interpreter output; currently they can receive partially stale input if
the test suite has previously been run. The solution is simply to remove
any old output from previous interpreter runs before we run them again.

Fixes #863

test/lit.cfg.py

@@ -129,9 +129,9 @@ def one_line(s):
         done
     ''')),
 
-    ('%run-binary-out', '%t.interpreter %test-input -1 %t.out.bin --binary-output'),
-    ('%run-binary', '%convert-input && %t.interpreter %t.bin -1 /dev/stdout'),
-    ('%run-proof-out', '%t.interpreter %test-input -1 %t.out.bin --proof-output'),
+    ('%run-binary-out', 'rm -f %t.out.bin && %t.interpreter %test-input -1 %t.out.bin --binary-output'),
+    ('%run-binary', 'rm -f %t.bin && %convert-input && %t.interpreter %t.bin -1 /dev/stdout'),
+    ('%run-proof-out', 'rm -f %t.out.bin && %t.interpreter %test-input -1 %t.out.bin --proof-output'),
     ('%run', '%t.interpreter %test-input -1 /dev/stdout'),
 
     ('%kprint-check', 'kprint %S %s true | diff - %s.out'),