switch regression/cbmc/Typecast2 to preprocessed code

This avoids the need for a cross-compiler to 64 bit when run on a 32-bit
system.

Author: kroening

regression/cbmc/Typecast2/main.c

@@ -0,0 +1,7 @@
+int main()
+{
+  unsigned int i=2;
+  __CPROVER_assert(0l==(signed long int)(i - (unsigned int)2),
+                   "difference of cast");
+  return 0;
+}

regression/cbmc/Typecast2/main.i

@@ -1,5 +1,5 @@
 CORE
-main.c
+main.i
 --no-propagation --64
 ^EXIT=0$
 ^SIGNAL=0$