How can I check if C++ and Fortran compiler works ?

[Dr. David Kirkby]

When I run a configure script I see this:

checking for gcc... gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes


but when it checks for g++ I see:

checking for g++... g++
checking whether we are using the GNU C++ compiler... yes
checking whether g++ accepts -g... yes
checking dependency style of g++... gcc3
checking how to run the C preprocessor... gcc -E


There is no actual test that the C++ compiler works. How can I add one? 
Currently in configure.ac I have these bits. (Obviously there is other stuff 
too, but


AC_CANONICAL_BUILD
AC_CANONICAL_HOST

#---------------------------------------------------------
#       C/C++/Fortran compilers


# First check for programs we need.
AC_LANG(C)
AC_LANG(C++)
AC_PROG_CC()
AC_PROG_CXX()
AC_PROG_CPP


I've noticed a bug report on the Sage mailing list

http://groups.google.com/group/sage-devel/browse_thread/thread/8030b427d6098ff2#

which looks to be that someone has g++ installed, but it does not actually work. 
My configure.ac script checks that there is not a mix of GNU and non-GNU 
compilers (for Solaris, HP-UX, AIX etc), and somehow my script is broken as it 
reports he has a mix of GNU and non-GNU compilers. In fact, I think his C++ 
compiler is probably broken, though I don't know for sure. But I don't have any 
test for it.

Dave