rustc: Disable rpath settings by default

This commit disables rustc's emission of rpath attributes into dynamic libraries
and executables by default. The functionality is still preserved, but it must
now be manually enabled via a `-C rpath` flag.

This involved a few changes to the local build system:

* --disable-rpath is now the default configure option
* Makefiles now prefer our own LD_LIBRARY_PATH over the user's LD_LIBRARY_PATH
  in order to support building rust with rust already installed.
* The compiletest program was taught to correctly pass through the aux dir as a
  component of LD_LIBRARY_PATH in more situations.

The major impact of this change is that neither rustdoc nor rustc will work
out-of-the-box in all situations because they are dynamically linked. It must be
arranged to ensure that the libraries of a rust installation are part of the
LD_LIBRARY_PATH. The default installation paths for all platforms ensure this,
but if an installation is in a nonstandard location, then configuration may be
necessary.

Additionally, for all developers of rustc, it will no longer be possible to run
$target/stageN/bin/rustc out-of-the-box. The old behavior can be regained
through the `--enable-rpath` option to the configure script.

This change brings linux/mac installations in line with windows installations
where rpath is not possible.

Closes #11747
[breaking-change]
Updated release notes for 0.11.0
Update AUTHORS.txt
Update to 0.11.0
librustc: Allow coercions through arrays.
rand: Small fix in parameter name

Documentation didn't match with parameter name.
Changes name of parameter in docs and function to 'amount'.
rustuv: Don't zero-out data on clones

When cloning a stream, the data is already guaranteed to be in a consistent
state, so there's no need to perform a zeroing. This prevents segfaults as seen
in #15231

Closes #15231
auto merge of #15246 : Sawyer47/rust/rand-doc-fix, r=alexcrichton

Documentation didn't match with parameter name.
Changes name of parameter in docs and function to 'amount'.
Wrap two code examples in backticks

This makes the docs ever-so-slightly easier to read.
librustc: Remove the fallback to `int` for integers and `f64` for
floating point numbers for real.

This will break code that looks like:

    let mut x = 0;
    while ... {
        x += 1;
    }
    println!("{}", x);

Change that code to:

    let mut x = 0i;
    while ... {
        x += 1;
    }
    println!("{}", x);

Closes #15201.

[breaking-change]
collections: minor cleanup
alloc: impl Default for Rc
core: optimize {option,result}::collect

The bug #11084 causes these collect functions to run about
twice as slow as they should because llvm is having trouble
optimizing away the closure for some reason. This patch works
around that performance bug by using a simple adapter iterator
explicitly for capturing if the outer iterator returns an
error.
auto merge of #15234 : pcwalton/rust/integer-fallback-and-casts, r=alexcrichton

This will break code that looks like:

    let mut x = 0;
    while ... {
        x += 1;
    }
    println!("{}", x);

Change that code to:

    let mut x = 0i;
    while ... {
        x += 1;
    }
    println!("{}", x);

Closes #15201.

[breaking-change]

r? @alexcrichton
auto merge of #15252 : alexcrichton/rust/issue-15231, r=pcwalton

When cloning a stream, the data is already guaranteed to be in a consistent
state, so there's no need to perform a zeroing. This prevents segfaults as seen
in #15231

Closes #15231
Extract tests from libcore to a separate crate

Libcore's test infrastructure is complicated by the fact that many lang
items are defined in the crate. The current approach (realcore/realstd
imports) is hacky and hard to work with (tests inside of core::cmp
haven't been run for months!).

Moving tests to a separate crate does mean that they can only test the
public API of libcore, but I don't feel that that is too much of an
issue. The only tests that I had to get rid of were some checking the
various numeric formatters, but those are also exercised through normal
format! calls in other tests.
auto merge of #15245 : sfackler/rust/coretest, r=alexcrichton

Libcore's test infrastructure is complicated by the fact that many lang
items are defined in the crate. The current approach (realcore/realstd
imports) is hacky and hard to work with (tests inside of core::cmp
haven't been run for months!).

Moving tests to a separate crate does mean that they can only test the
public API of libcore, but I don't feel that that is too much of an
issue. The only tests that I had to get rid of were some checking the
various numeric formatters, but those are also exercised through normal
format! calls in other tests.
it -> Cargo

It wasn't clear if we needed to install Hello World or Cargo.
auto merge of #15254 : alex/rust/patch-1, r=alexcrichton

This makes the docs ever-so-slightly easier to read.
auto merge of #15256 : erickt/rust/optimizations, r=alexcrichton

The bug #11084 causes `option::collect` and `result::collect` about twice as slower as it should because llvm is having some trouble optimizing away the scan closure. This gets rid of it so now those functions perform equivalent to a hand written version.

This also adds an impl of `Default` for `Rc` along the way.