[CGSCCPassManagerTest] Replace no-op bitcast to create constant using the old function (#72460)

With opaque pointers enabled, the existing ptr-to-ptr bitcast is a no-op
and no longer creates a constant that references the old function.

Replace the no-op bitcast with code that creates a constant that
references the old function. The test now fails if the 1 new line of
code added to `CallGraphUpdater::replaceFunctionWith()` in
cb0ecc5 is removed (test passes if kept
intact).

---------

Co-authored-by: Nikita Popov <[email protected]>

Author: JOE1994

llvm/unittests/Analysis/CGSCCPassManagerTest.cpp

@@ -1631,10 +1631,9 @@ TEST_F(CGSCCPassManagerTest, TestUpdateCGAndAnalysisManagerForPasses8) {
           FnF->getEntryBlock().front().moveBefore(RI);
         ASSERT_NE(FnF, nullptr);
 
-        // Create an unsused constant that is referencing the old (=replaced)
+        // Create an unused constant that is referencing the old (=replaced)
         // function.
-        ConstantExpr::getBitCast(FnF,
-                                 PointerType::getUnqual(FnF->getContext()));
+        ConstantExpr::getPtrToInt(FnF, Type::getInt64Ty(FnF->getContext()));
 
         // Use the CallGraphUpdater to update the call graph.
         CallGraphUpdater CGU;