My earlier patch to compile stage 1 with -std=c++98 ran into trouble on 
FreeBSD, where that flag suppresses declaration of C99 library functions 
like strtoull.  I was surprised that configure was seeing the 
declaration, but discovered that this was because configure was using 
the C compiler rather than the C++ compiler.  This patch changes GCC 
configury to always use C++, and to use the normal AC_CHECK_DECLS for 
overloaded functions.

OK for trunk?

Jason