Spec: allow --link-flags to be used

[bcardiff]

Fix #6231 .

The --link-flags is not added in the setup_simple_compiler_options because setting the compiler.link_flags is done after the OptionParser.parse.

Nevertheless the setup_simple_compiler_options is used for crystal eval and crystal spec only.
I don't think --link-flags are needed for eval

[RX14]

--link-flags does make sense for eval, because the resulting executable is linked and executed normally.

[bcardiff]

they make sense yes, but is there a use case for that?

[faustinoaq]

@bcardiff @RX14 maybe this: (oneliner server like python -m http.server on macOS)

crystal eval 'server=HTTP::Server.new(HTTP::StaticFileHandler.new("."));server.listen(8080)' --link-flags -L/usr/local/opt/openssl/lib

[asterite]

What is the --link-flags used for?

[RX14]

@bcardiff when you need extra link flags to make an executable run at all? Perhaps you just want to run a quick snippet like require "myshard"; MyShard.foo, but you want to test the snippet against two seperately installed versions of a C library.

Why not allow it, if it's pretty much easier to allow it than disallow it, by placing the option where the rest of the shared compiler flags are anyway?

[RX14]

Oh, I misread the OP. I thought you were keeping --link-flags out of setup_simple_compiler_options because you specifically didn't want it on eval, not just for technical reasons. Surely we could do something like compiler.link_flags += " #{link_flag}" in the handler and put it in setup_simple_compiler_options...