Make fuse_main_real() not symboled

Make fuse_main_real() not symboled

Addresses https://github.com/libfuse/libfuse/issues/1092

We actually don't need to make fuse_main_real() symboled, as it
is not part of the official API.

The inlined function now always calls into fuse_main_real_317
and the compat ABI function (which should also be available
for dlopen/dlsym) is now always compiled, independent if the
compiler/linker support versioned symbols.

Additionally, fuse_main_real() is also declared as inlined
function and a warning message is created when that function
is called.

Signed-off-by: Bernd Schubert <bernd@bsbernd.com>