The GNU C compiler apparently still permits this, and the VC++ 2005 compiler permits it too, though it issues a Level-4 warning if it’s C code, and a Level-2 warning if it’s C++ code.
I. Sason, and S. Verdú. (2015)cite arxiv:1508.00335Comment: IEEE Trans. on Information Theory, vol. 62, no. 11, pp. 5973--6006, November 2016. This manuscript is identical to the journal paper, apart of some additional material which includes Sections III-C and IV-F, and three technical proofs.