/lib/libgcc_s.so.1: version GCC_4.6.0 required by /usr/local/lib/gcc47/libgfortran.so.3 not found

I replaced lang/gcc46 by lang/gcc47, since gcc46 doesn't build anymore
on the FreeBSD 10.0-CURRENT in question.

I have a small f77 program, which built well with the autotools I used
and ran for ages now. But I receive this error:

/lib/libgcc_s.so.1: version GCC_4.6.0 required by
/usr/local/lib/gcc47/libgfortran.so.3 not found

when compiled with gfortran47.

The autotool environment complains about it can not run Fortran 77
compiled programs, as the error below shows. What happened here?

ohartmann_at_thor: [prog] ./configure
checking for gfortran47... gfortran47
checking whether the Fortran 77 compiler works... yes
checking for Fortran 77 compiler default output file name... a.out
checking for suffix of executables...
checking whether we are cross compiling... configure: error: in
`/home/ohartmann/Projects/prog':
configure: error: cannot run Fortran 77 compiled programs.
If you meant to cross compile, use `--host'.
See `config.log' for more details