since we refer to C++ later in configure, we need to search for the prog

http://bugs.gentoo.org/212772

--- configure.in
+++ configure.in
@@ -30,6 +30,7 @@
 AC_ISC_POSIX
 AC_PROG_CC
 AM_PROG_CC_C_O
+AC_PROG_CXX
 AC_HEADER_STDC
 AC_PROG_LIBTOOL
 AC_PROG_MAKE_SET