AM_PATH_GTK_2_0 fails for c++ programs

[rsteinke w-link net]

I've encounted a bug where AM_PATH_GTK_2_0 will fail in
a configure script for a c++ program (i.e., where AC_INIT
was called with a .cpp file). In this case, the call to
AC_TRY_RUN inside AM_PATH_GTK_2_0 uses CXXFLAGS instead of
CFLAGS. Since only CFLAGS is set, it fails to see the
gtk headers, and reports that it can't find gtk.

It seems like the fix could simply set CXXFLAGS as well
as CFLAGS. I'm not sure if the m4 file is dynamically
generated, though, so I don't know where to put the fix.

Ron Steinke