remove dead link to rustpkg documentation
Tweak test name and make it more specific
Add ignore-cross-compile directive for compiletest

Loadable syntax extensions don't work when cross compiling (see #12102), so the
fourcc tests all need to be ignored. They're valuable tests, so they shouldn't
be outright ignored, so they're now flagged with ignore-cross-compile
auto merge of #12184 : JeremyLetang/rust/rustpkg-link, r=alexcrichton
auto merge of #12185 : nikomatsakis/rust/issue-12033-tweak-test, r=alexchrichton
auto merge of #12190 : alexcrichton/rust/fix-snap-again, r=brson

Loadable syntax extensions don't work when cross compiling (see #12102), so the
fourcc tests all need to be ignored. They're valuable tests, so they shouldn't
be outright ignored, so they're now flagged with ignore-cross-compile
Removed ty_type (previously used to represent *tydesc).