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.
S. Maxwell. Late Breaking Papers at the Genetic Programming 1996
Conference Stanford University July 28-31, 1996, page 125--128. Stanford University, CA, USA, Stanford Bookstore, (28--31 July 1996)
D. Howard. Late Breaking Papers at the Genetic Programming 1998
Conference, University of Wisconsin, Madison, Wisconsin, USA, Stanford University Bookstore, (22-25 July 1998)