Using an invalid recursive Enum crashed the compiler due to running out of stack

[DoctorAlpaca]

This snippet:

enum Outer {
    Y(Inner)
}

enum Inner {
    X(Inner)
}

Crashes the compiler without further error description. My output with further details:

$ RUST_LOG=rustc=1,::rt::backtrace rustc main.rs 
rust: task 7f757c2084c0 ran out of stack
/usr/lib/librustrt.so(_ZN9rust_task13begin_failureEPKcS1_m+0x4b)[0x7f758487464b]
/usr/lib/librustrt.so(_ZN9rust_task9new_stackEm+0x215)[0x7f7584874b85]
/usr/lib/librustrt.so(+0x2a189)[0x7f7584885189]
/usr/lib/librustrt.so(upcall_new_stack+0x241)[0x7f7584876eb1]
/usr/lib/librustc-c84825241471686d-0.6.so(+0x8b8aca)[0x7f7586a42aca]
/usr/lib/librustc-c84825241471686d-0.6.so(_ZN6middle2ty13enum_variants17_cf5df85c66f3dde53_06E+0x87)[0x7f7586297407]
/usr/lib/librustc-c84825241471686d-0.6.so(_ZN6middle2ty26type_structurally_contains16_e4dc723a9d111e73_06E+0x1f9)[0x7f75865121a9]
/usr/lib/librustc-c84825241471686d-0.6.so(+0x38881b)[0x7f758651281b]
/usr/lib/librustc-c84825241471686d-0.6.so(_ZN6middle2ty26type_structurally_contains16_e4dc723a9d111e73_06E+0x2af)[0x7f758651225f]
/usr/lib/librustc-c84825241471686d-0.6.so(+0x38881b)[0x7f758651281b]
/usr/lib/librustc-c84825241471686d-0.6.so(_ZN6middle2ty26type_structurally_contains16_e4dc723a9d111e73_06E+0x2af)[0x7f758651225f]
/usr/lib/librustc-c84825241471686d-0.6.so(+0x38881b)[0x7f758651281b]

{ A lot more of that }

error: internal compiler error: unexpected failure
note: the compiler hit an unexpected failure path. this is a bug
note: try running with RUST_LOG=rustc=1,::rt::backtrace to get further details and report the results to github.com/mozilla/rust/issues
rust: task failed at 'explicit failure', /build/src/rust-0.6/src/librustc/rustc.rc:357
/usr/lib/librustrt.so(_ZN9rust_task13begin_failureEPKcS1_m+0x4b)[0x7f758487464b]
/usr/lib/librustrt.so(+0x2a189)[0x7f7584885189]
/usr/lib/librustrt.so(upcall_fail+0x198)[0x7f75848763a8]
/usr/lib/libcore-c3ca5d77d81b46c1-0.6.so(+0x1055db)[0x7f7587a7c5db]
/usr/lib/libcore-c3ca5d77d81b46c1-0.6.so(+0x105582)[0x7f7587a7c582]
/usr/lib/libcore-c3ca5d77d81b46c1-0.6.so(_ZN3sys12begin_unwind17_61fe198059b9e3fc3_06E+0x71)[0x7f75879c4651]
/usr/lib/libcore-c3ca5d77d81b46c1-0.6.so(+0x14dcb4)[0x7f7587ac4cb4]
/usr/lib/librustc-c84825241471686d-0.6.so(_ZN7monitor17_78935df9ff9e1afa3_06E+0x1577)[0x7f7586a365f7]
/usr/lib/librustc-c84825241471686d-0.6.so(+0x8b8b34)[0x7f7586a42b34]
/usr/lib/librustc-c84825241471686d-0.6.so(_ZN4main15_c4de63b748e03d3_06E+0x7e)[0x7f7586a4274e]
/usr/lib/librustrt.so(_Z18task_start_wrapperP10spawn_args+0x24)[0x7f7584874e64]
rust: domain main @0x1dbe3c0 root task failed

[catamorphism]

Dup of #3008