That macro dates back to /usr/include header files that would play
tricks like this
#define _IO(n, x) (('n'<<8)+x)
#define TIOCFOO _IO(T, 1)
and would expect TIOCFOO to be equivalent to (('T'<<8)+1). This sort of
trick worked with K&R C compilers but does not work with C89+. To work
around the problem back in the day, you needed to use 'gcc -traditional'.
Using -traditional had obvious problems, though, so GCC soon changed its
installation procedure "fixincludes" to make fixed copies of these
K&R-assuming headers during installation, and to compile by including
the fixed copies. This was around 1990. I was involved with some of that
header-munging effort but have blessedly forgotten most of the details.
A descendant of the fixincludes work is still in GCC's source code
(which is where I got the above example).
AC_PROG_GCC_TRADITIONAL has not been needed for thirty years, and was
declared obsolescent in Autoconf 2.60 (2006-06-05). Also, the Autoconf
manual (as of the next version) states Autoconf assumes C89 or later. So
if there's any issue with AC_PROG_GCC_TRADITIONAL at all, I suggest
replacing its definition with:
AU_DEFUN([AC_PROG_GCC_TRADITIONAL])
and updating documentation and tests and etc. accordingly.
