rustc: Remove 'morestack_addr' intrinsic. Unused
Set the LD_LIBRARY_PATH when running tests

This way when you disable rpaths you can still run `make check`
auto merge of #12099 : alexcrichton/rust/rpath-tests, r=thestinger

This way when you disable rpaths you can still run `make check`
auto merge of #12086 : huonw/rust/safe-json, r=kballard

The lexer and json were using `transmute(-1): char` as a sentinel value for EOF, which is invalid since `char` is strictly a unicode codepoint.

Fixing this allows for range asserts on chars since they always lie between 0 and 0x10FFFF.
auto merge of #12096 : brson/rust/morestack-addr, r=thestinger
std: Rename `assert` and `assert_eq` to `enforce` and `enforce_eq`.

These macros are always enabled so there's no particular need to fly in
the face of established convention where assertions are removed in
production code.

Closes #12049.
std: add `debug_assert!` and `debug_assert_eq!`, only active for --cfg debug.
Rename uses of `assert!` to `enforce!`.
Rename uses of `assert_eq!` to `enforce_eq!`.