Cfgs from build script not passed to rustdoc

[gkoz]

The cfg directives returned by the build script via the cargo:rustc-cfg=foo convention are not passed to rustdoc when invoking cargo doc.

rustdoc seems to accept them just fine i.e. invoking it manually with --cfg foo produces the expected results.

[alexcrichton]

I think this is a dupe of #1277, but thanks for the report!

[gkoz]

Not really. #1277 talks about features only (so a subset of cfg functionality). It appears to have been fixed back then.

[alexcrichton]

Hm, good point. I could of sworn we had a few dupes for this issue, but I guess this one will now become the "one true issue"!