oeqa/buildoptions: check that Fortran code actually cross-compiles

oeqa/buildoptions: check that Fortran code actually cross-compiles

Don't just test that we can build the cross-compiler, but test that it actually
can cross-compile some Fortran.

The quadmath dependency is now handled in gcc-runtime and isn't needed in this
test (as per local.conf.sample.extended changes).

There's also no need to build libgfortran explicitly, as fortran-helloworld depends on it.

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>