rustc: Start accepting `*const T`

This does not yet change the compiler and libraries from `*T` to `*const T` as
it will require a snapshot to do so.

cc #7362
librustc: Don't overwrite vtables when coercing to trait object.
Mark all crates except std as experimental
Fix spans for doc comments
Remove obsolete test

This test was added long time ago and marked as ignored.
The same test was added later in #8485 as run-fail/issue-3907.rs,
but the old one was not deleted.
Don't require mutable StringReader to emit lexer errors

Teach StringReader how to emit errors for arbitrary spans, so we don't
need to modify peek_span. This allows for emitting errors without having
a &mut borrow of the StringReader.
test: Attempt to fix nightly-linux

The nightly builds on linux have been failing over the past few days due to a
malformed LD_LIBRARY_PATH. It appears that the underlying cause is that one of
the tests, dep-info-custom, recursively invokes make but the RUSTC variable
passed down has the string "$LD_LIBRARY_PATH". This is intended to read the
host's original LD_LIBRARY_PATH, but it appears that the makefile is eagerly
expanding the "$L" to nothing, causing the original host's LD_LIBRARY_PATH to be
ignored.

This fix removes passing the string "$LD_LIBRARY_PATH" and rather expands it
eagerly to ensure that escaping doesn't happen at a later stage. I'm still not
entirely sure why the makefile is interpreting the dollar as a variable, but
this seems to fix the issue.
auto merge of #15006 : alexcrichton/rust/fix-nightly, r=brson

The nightly builds on linux have been failing over the past few days due to a
malformed LD_LIBRARY_PATH. It appears that the underlying cause is that one of
the tests, dep-info-custom, recursively invokes make but the RUSTC variable
passed down has the string "$LD_LIBRARY_PATH". This is intended to read the
host's original LD_LIBRARY_PATH, but it appears that the makefile is eagerly
expanding the "$L" to nothing, causing the original host's LD_LIBRARY_PATH to be
ignored.

This fix removes passing the string "$LD_LIBRARY_PATH" and rather expands it
eagerly to ensure that escaping doesn't happen at a later stage. I'm still not
entirely sure why the makefile is interpreting the dollar as a variable, but
this seems to fix the issue.
vim: Add :Run and :Expand commands

Define a command :Run to compile and run the current file. This supports
unnamed buffers (by writing to a temporary file). See the comment above
the command definition for notes on usage.

Define <D-r> and <D-R> mappings for :Run to make it easier to invoke in
MacVim.

Define a command :Expand to display the --pretty expanded output for the
current file. This can be configured to use different pretty types. See
the comment above the command definition for notes on usage.

Create an autoload file and put function definitions there to speed up
load time.
Rename :Run and :Expand to :RustRun and :RustExpand
Write documentation for the Rust vim plugin
Add commands :RustEmitIr and :RustEmitAsm
Add a ByteOrder trait for abstracting over endian conversions

The `Bitwise::swap_bytes` method was also moved into the `ByteOrder` trait. This was because it works on the byte level rather than the bit level.
Use ByteOrder methods instead of free-standing functions
Fix comment formatting
Merge the Bitwise and ByteOrder traits into the Int trait

This reduces the complexity of the trait hierarchy.
Remove `#[stable]` attribute from free-standing endian conversions and mark them as deprecated
Shorten endian conversion method names

The consensus on #14917 was that the proposed names were too long.
Update doc comment for Int trait
librustc: Use expr_ty_adjusted in trans_overloaded_call.