testsuite: Remove xfail from g++.dg/ipa/devirt-23.C [PR60674]

As Andrew Pinski noted in PR60674:

  devirt-23.C started to pass with r16-101-g132d01d96ea9d6.

  So just need to update the testcase removing the xfail and close this
  bug as fixed.

  The reason why this was not fixed until r16-101-g132d01d96ea9d6 is
  because the call is from main which is known to be called once and was
  not a candidate for IPA-CP until then.

  In fact renaming the function from main to f (and adding a `return 0`
  so not invoking undefined behavior), the scan-ipa-dump works all the
  way back to GCC 5.

Tested on aarch64-linux-gnu and arm-linux-gnueabihf.

gcc/testsuite/ChangeLog:
	PR ipa/60674
	* g++.dg/ipa/devirt-23.C: Remove xfail.