test: Remove run-pass/too-much-recursion.rs

I don't understand how this is still passing on the bots. This condition
should trigger an abort now.
The null case of a nullable-poiner enum might not be nullary.

Cases like `Either<@int,()>` have a null case with at most one value but
a nonzero number of fields; if we misreport this, then bad things can
happen inside of, for example, pattern matching.

Closes #6117.
Reverse accidental src/llvm reversion in 876483dcf, and add test.

The test is reduced from a doc test, but making it separate ensures that
(1) unrelated changes to the docs won't leave this case uncovered, and
(2) the nature of any future failures will be more obvious to whoever
sees the tree on fire as a result.
Revert "doc: XFAIL mysterious failure on bots"

This reverts commit 2c6dae081b72d33a2c51b5f46436e6350bb3682f.
auto merge of #6118 : brson/rust/too-much-recursion, r=thestinger

I don't understand how this is still passing on the bots. This condition
should trigger an abort now.
auto merge of #6134 : jld/rust/issue-6117, r=catamorphism

Cases like `Either<@int,()>` have a null case with at most one value but
a nonzero number of fields; if we misreport this, then bad things can
happen inside of, for example, pattern matching.

Closes #6117.
auto merge of #6136 : jld/rust/simplifycfg-unrevert, r=thestinger

Also add the clearly marked test case that should have been there all along, and un-xfail the not-so-obvious doc test that was affected.