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]
Guide: complex data types
Guide: comments
webfonts: proper fix
webfonts: serve Source Code Pro locally

So that we have freestanding docs.
webfonts: check-in licenses
auto merge of #14832 : alexcrichton/rust/no-rpath, r=brson

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]
auto merge of #15374 : steveklabnik/rust/comments, r=brson

I'm leaving off `rustdoc` usage because it won't work unless this is a `pub fn`, and I want to talk about public/private in the context of modules. I'm also not mentioning `//!` because it is exclusively used to provide the overview of a module.
Removing recursion from find_mut in treemap
auto merge of #15422 : steveklabnik/rust/guide_compound_data_types, r=brson

I'm not happy about the hand-waving around `cmp`, but I'm not sure how to get around it.
auto merge of #15537 : jbclements/rust/hygiene-for-methods, r=pcwalton

This patch adds hygiene for methods. This one was more difficult than the others, due principally to issues surrounding `self`. Specifically, there were a whole bunch of places in the code that assumed that a `self` identifier could be discarded and then made up again later, causing the discard of contexts and hygiene breakage.
Add example to Any documentation
syntax: doc comments all the things
token: replace ast::Ident with just Ident
testsuite: merge some lexer testcases

Now that the lexer is more robust, these tests don't need to be in separate
files. Yay!
str: use more helpful assertion failure messages
test: simplify numeric literal cfail tests
syntax: use a better Show impl for Ident

Rather than just dumping the id in the interner, which is useless, actually
print the interned string. Adjust the lexer logging to use Show instead of
Poly.
codemap: be less annoying in debug logging
lexer: shuffle around some functions