double underscores in autoconf-defined symbol names

[Vadim Zeitlin]

 Hello,

 I'd like to know if there is any standard way of dealing with a problem
which arises when you use AC_CHECK_FUNCS with a function whose name begins
with an underscore (e.g. _snprintf) and then use the result of the test in
C++ code. To be precise, the problem is that AC_CHECK_FUNCS would define a
symbol HAVE__SNPRINTF which, according to 17.4.3.1.2 of the ISO C++
standard, is a reserved symbol in C++ program and so can't be used.

 Of course, it's pretty simple to work around this problem by using
AC_CHECK_FUNC instead but as I'm surely not the first one to be in such
situation, I'd like to know:

1. What do the others do? Just ignore this problem (hoping that HAVE__XXX
   is not really reserved) or is there something better?
2. Is there any more or less standard convention for naming HAVE symbol for
   such functions (HAVE_UNDERSCORE_SNPRINTF looks a bit ugly)?
3. Is it worth looking into patching autoconf to change AC_CHECK_FUNCS to
   not generate reserved symbols for such functions or if such patch would
   not be accepted anyhow (e.g. because of backwards compatibility)?

 Thanks in advance,
VZ