This commit is an implementation of [RFC 1513] which allows applications to
alter the behavior of panics at compile time. A new compiler flag, `-C panic`,
is added and accepts the values `unwind` or `panic`, with the default being
`unwind`. This model affects how code is generated for the local crate, skipping
generation of landing pads with `-C panic=abort`.
[RFC 1513]: https://github.com/rust-lang/rfcs/blob/master/text/1513-less-unwinding.md
Panic implementations are then provided by crates tagged with
`#![panic_runtime]` and lazily required by crates with
`#![needs_panic_runtime]`. The panic strategy (`-C panic` value) of the panic
runtime must match the final product, and if the panic strategy is not `abort`
then the entire DAG must have the same panic strategy.
With the `-C panic=abort` strategy, users can expect a stable method to disable
generation of landing pads, improving optimization in niche scenarios,
decreasing compile time, and decreasing output binary size. With the `-C
panic=unwind` strategy users can expect the existing ability to isolate failure
in Rust code from the outside world.
Organizationally, this commit dismantles the `sys_common::unwind` module in
favor of some bits moving part of it to `libpanic_unwind` and the rest into the
`panicking` module in libstd. The custom panic runtime support is pretty similar
to the custom allocator support with the only major difference being how the
panic runtime is injected (takes the `-C panic` flag into account).
Currently the nightlies we're producing fail when linking some C code into a
Rust application with the error message:
libgcc_s.so.1: error adding symbols: DSO missing from command line
By linking `gcc_s` instead of `gcc` this error goes away. I haven't tested this
on NetBSD itself, but should help get the Linux cross-compile image moreso up
and working!
Was getting error:
```
running: "sh" "/home/flubba86/rust/src/libstd/../libbacktrace/configure" "--with-pic" "--disable-multilib" "--disable-shared" "--disable-host-shared" "--host=asmjs-unknown-emscripten" "--build=x86_64-unknown-linux-gnu"
...
Invalid configuration `asmjs-unknown-emscripten': system `emscripten' not recognized
```
Undo change to libbacktrace configure script.
Modify libstd build.rs to not build libbacktrace in the case of targeting emscripten.
Have all Cargo-built crates pass `--cfg cargobuild` and then add appropriate
`#[cfg]` definitions to all crates to avoid linking anything if this is passed.
This should help allow libstd to compile with both the makefiles and with Cargo.
This commits adds build scripts to the necessary Rust crates for all the native
dependencies. This is currently a duplication of the support found in mk/rt.mk
and is my best effort at representing the logic twice, but there may be some
unfortunate-and-inevitable divergence.
As a summary:
* alloc_jemalloc - build script to compile jemallocal
* flate - build script to compile miniz.c
* rustc_llvm - build script to run llvm-config and learn about how to link it.
Note that this crucially (and will not ever) compile LLVM as that would take
far too long.
* rustdoc - build script to compile hoedown
* std - script to determine lots of libraries/linkages as well as compile
libbacktrace
