Version-gate appending -syslibroot flag to lld

[kubkon]

This commit version-gates appending -syslibroot flag to lld. This
is predicated upon the fact that for versions of macOS lower than
11, lld would fail to find and link against frameworks with this
flag specified.

Closes#6996

Co-authored-by: Andrew Kelley andrew@ziglang.org

[kubkon]

cc @mkeeter, if you could rebase onto this branch and lemme know if this fixes the linking issues for you, that'd be grand!

[andrewrk]

cc @mkeeter, if you could rebase onto this branch and lemme know if this fixes the linking issues for you, that'd be grand!

I'm going to optimistically merge this & close the issue, so that there will be a binary available for testing with these changes in a couple hours. Of course please do let us know if there is still a problem.

[mkeeter]

Thanks, I'll check out the auto-built binary this weekend (I haven't gone far enough down the rabbit hole to be building Zig from source on my own machine 😆)

[kubkon]

Thanks, I'll check out the auto-built binary this weekend (I haven't gone far enough down the rabbit hole to be building Zig from source on my own machine 😆)

Oh no, you’re missing all the fun!

[mkeeter]

Confirmed that this now works on my machine!

Strangely, upgrading did broke a post-build step which runs install_name_tool on the resulting binary, due to complaints about signing. I don't think this is a Zig issue, though, and I worked around this by renaming the relevant dylib itself.