When CXX is specified, configure does not report that it is looking for a C++ compiler, nor its answer.
$ cat configure.ac AC_INIT AC_PROG_CC AC_PROG_CXX $ autoconf $ diff -U 100 =(./configure) =(./configure CC=gcc CXX=g++) --- /tmp/zshIZDChp 2012-10-26 13:39:32.000000000 +0200 +++ /tmp/zshIxgQgH 2012-10-26 13:39:33.000000000 +0200 @@ -1,12 +1,11 @@ checking for gcc... gcc checking whether the C compiler works... yes checking for C compiler default output file name... a.out checking for suffix of executables... checking whether we are cross compiling... no checking for suffix of object files... o checking whether we are using the GNU C compiler... yes checking whether gcc accepts -g... yes checking for gcc option to accept ISO C89... none needed -checking for g++... g++ checking whether we are using the GNU C++ compiler... yes checking whether g++ accepts -g... yes FWIW, I think configure should say "checking for a C++ compiler", "checking for a C compiler" instead of "checking for gcc".
