We currently have no need for the frame pointers on any platform. They
may eventually be needed on platforms without an equivalent to the DWARF
call frame information to walk the stack in the garbage collector.

Closes #7477

This PR contains some code cleanup and the fix for issue #8670.
~~I am not sure about issue #8442 (could not reproduce it). @jdm, could check after this is merged and possibly close the issue then?~~ (closed now)

Some interesting facts: With this commit, it should be possible to compile libstd with `-Zdebug-info` (it does not work yet with `-Zextra-debug-info` but we are getting there). Switching debug info on increases the compile time for libstd by about 2 seconds.

@catamorphism I get one failing test in rustpkg:
`package_script_with_default_build` says: `task <unnamed> failed at 'Couldn't copy file', /home/mw/rust/src/librustpkg/tests.rs:689`
Would you have any idea what that is about? Seems be something wrong on my machine...

Cheers,
Michael

Fixes #8670

The FFI tutorial still incorrectly stated that strings were terminated
with 

Resolves #8687.

r anybody; there isn't anything complicated here

r? @thestinger

This resolves issue #908.  

Notable changes:
-  On Windows, LLVM integrated assembler emits bad stack unwind tables when segmented stacks are enabled.  However, unwind info directives in the assembly output are correct, so we generate assembly first and then run it through an external assembler, just like it is already done for Android builds.

- Linker is invoked  via "g++" command instead of "gcc": g++ passes the appropriate magic parameters to the linker, which ensure correct registration of stack unwind tables in dynamic libraries.

Attempt #2 of [this pull request](https://github.com/mozilla/rust/pull/8597) since my tired mind decided messing up my repo, then deleting and re-forking was a good idea.  This is identical to the second last commit in that PR.  (The one before I ruined everything.)

This is an improvement to use_decl docs, which will hopefully improve understanding of how resolution works and where `extern mod` and module declarations should go to make them visible to use declarations.

removed pub on real_args, changed test to use args

This PR includes the addition of the essential CRUD functionality exposed as a part of the `uv_fs_*` api. There's a lot more to be done, but the essential abstractions are in place and can be easily expanded.

A summary:

* `rt::io::file::FileStream` is fleshed out and behaves as a *non-positional* file stream (that is, it has a cursor that can be viewed/changed via `tell` and `seek`
* The underlying abstraction in `RtioFileStream` exposes pairs of `read(), write()` and `pread(), pwrite()`. The latter two take explicit `offset` params and don't respect the current cursor location in a file afaik. They both use the same underlying libuv impl
* Because libuv explicitly does *not* support `seek`/`tell` operations, these are impl'd in `UvFileStream` by using `lseek(2)` on the raw file descriptor.
* I did my best to flesh out and adhere to the stubbing that was already present in `rt::io::file` and the tests should back that up. There may be things missing.
* All of the work to test `seek`/`tell` is done in `rt::io::file`, even though the actual impl is down in `rt::uv::uvio`.
* We have the ability to spin up an `~RtioFileStream` from a raw file descriptor. This would be useful for interacting with stdin and stdout via newrt.
* The lowest level abstractions (in `rt::uv::file`) support fully synchronous/blocking interactions with the uv API and there is a CRUD test using it. This may also be useful for blocking printf, if desired (the default would be non-blocking and uses libuv's io threadpool)

There are a few polish things I need to do still (the foremost that I know of is undefined behavior when seek'ing beyond the file's boundary).

After this lands, I want to move on to mapping more of the `uv_fs_*` API (especially `uv_fs_stat`). Also a few people have mentioned interest in `uv_pipe_t` support. I'm open to suggestions.

We currently have no need for the frame pointers on any platform. They
may eventually be needed on platforms without an equivalent to the DWARF
call frame information to walk the stack in the garbage collector.

Closes #7477

using this to turn off the frame pointers isn't needed, and doesn't
actually work right now because the reference to it omits the target
triple

The FFI tutorial still incorrectly stated that strings were terminated
with \0 and suggested using `str::as_c_str`.