Define YP_EXPORTED_FUNCTION as empty

[tenderlove]

We are currently leaking YARP symbols in Ruby 3.3 (Ruby head):

$ nm libruby.3.3-static.a | grep yp_parser_init
000000000000000c T _yp_parser_init
000000000002a393 s l___func__.yp_parser_init

This is not good because if we use Ruby 3.3 to compile YARP as a C
extension (for example installing the YARP gem), the linker gets
confused and ends up prioritizing the symbol found in Ruby rather than
the one from the Gem. This means the C extension can end up calling in
to yp_parser_init in Ruby rather than the new one shipped with the
extension.

If I use current Ruby head to compile YARP in this repository, nm will
show that yp_parser_init is not defined:

$ nm lib/yarp.bundle | grep yp_parser_init
                 U _yp_parser_init

This is because the linker got confused about the leaked symbols.

I would like to default all functions to not be external. This hides
the symbols and fixes the problem with Ruby and YARP as a gem. If I
apply this patch to Ruby, build Ruby, then build YARP, yp_parser_init
is defined in the Gem:

$ nm lib/yarp.bundle | grep yp_parser_init
00000000000162f8 t _yp_parser_init
000000000002d8ac t _yp_parser_init.cold.1
000000000002d8d4 t _yp_parser_init.cold.2

/cc @flavorjones

Related to #1110

[kddnewton]

I think at this point with this PR you can just remove the whole macro. If the point is that nothing should be exported let's get rid of the whole thing and just keep visibility hidden.

[eregon]

We need the symbols to be exported for the dynamic library, for Fiddle/FFI: #1112

[eregon]

Could Ruby define YP_STATIC to avoid exporting the symbols? Or use the librubyparser.a?

[flavorjones]

Yeah, just for the record: #1069 set up compilation so that compiling with -DYP_STATIC would hide symbols. This is how librubystatic.a is being built on yarp:main right now.

It seems like we have two options:

1. downstream in Ruby, make sure YARP is compiled with -DYP_STATIC
2. make static (hidden symbols) the default (what this PR chooses to do)

I don't care which; but if we choose 2 then we need to make sure librubyparser.so is being built so that symbols are shared, which this PR isn't doing:

$ nm build/librubyparser.so | fgrep yp_parse
0000000000021780 t yp_parse
0000000000021800 t yp_parse_serialize
00000000000216d0 t yp_parser_free
0000000000021440 t yp_parser_init
0000000000005620 t yp_parser_local_depth.isra.0
0000000000005550 t yp_parser_parameter_name_check
00000000000216b0 t yp_parser_register_encoding_changed_callback
00000000000216c0 t yp_parser_register_encoding_decode_callback

Compare that output to what gets built on main right now:

$ nm build/librubyparser.so | fgrep yp_parse
0000000000021830 T yp_parse
00000000000026d1 t yp_parse.cold
00000000000219f0 T yp_parse_serialize
0000000000021780 T yp_parser_free
00000000000214f0 T yp_parser_init
0000000000005820 t yp_parser_local_depth.isra.0
0000000000005750 t yp_parser_parameter_name_check
0000000000021760 T yp_parser_register_encoding_changed_callback
0000000000021770 T yp_parser_register_encoding_decode_callback

[eregon]

Yeah I'd be totally fine to change the default, just as you said the .so should have exported symbols, the rest shouldn't.

[tenderlove]

2. make static (hidden symbols) the default (what this PR chooses to do)

Yes, I'd like to do this one because I don't really want to modify the build system in Ruby.

[flavorjones]

@tenderlove I think you can close this now that #1110 shipped.

[jemmaissroff]

Closing since #1110 shipped