Fix typos

Author: peterschrammel

src/goto-symex/symex_assign.cpp

@@ -43,7 +43,7 @@ void goto_symext::symex_assign(
 
       DATA_INVARIANT(
         !side_effect_expr.operands().empty(),
-        "function call stamement expects non-empty list of side effects");
+        "function call statement expects non-empty list of side effects");
 
       DATA_INVARIANT(
         function_call.function().id() == ID_symbol,

src/goto-symex/symex_goto.cpp

@@ -468,7 +468,7 @@ static void merge_names(
   // Don't add a conditional to the assignment when:
   //  1. Either guard is false, so we can't follow that branch.
   //  2. Either identifier is of generation zero, and so hasn't been
-  //     initialized and therefor an invalid target.
+  //     initialized and therefore an invalid target.
   if(dest_state.guard.is_false())
     rhs = goto_state_rhs;
   else if(goto_state.guard.is_false())