Auto merge of #36339 - brson:emscripten-new, r=alexcrichton

Working asmjs and wasm targets

This patch set results in a working standard library for the asmjs-unknown-emscripten and wasm32-unknown-emscripten targets. It is based on the work of @badboy and @rschulman.

It does a few things:

- Updates LLVM with the emscripten [fastcomp](https://github.com/rust-lang/llvm/pull/50) patches, which include the pnacl IR legalizer and the asm.js backend. This patch is thought not to have any significant effect on existing targets.
- Teaches rustbuild to correctly link C code with emscripten
- Updates gcc-rs to work correctly with emscripten
- Teaches rustbuild to run crate tests for emscripten with node
- Modifies Thread::new to return an error on emscripten, to facilitate debugging a common failure mode
- Modifies libtest to run in single-threaded mode for emscripten
- Ignores a host of tests that don't work yet, mostly dealing with threads and I/O
- Updates libc with wasm32 definitions (presently the same as asmjs)
- Adds a wasm32-unknown-emscripten target that feeds the output of LLVM's asmjs backend through emcc to generate wasm

Notes and caveats:

- This is only known to work with `--enable-rustbuild`.
- The wasm32 target can't be tested correctly yet because of issues in compiletest and limitations in node https://github.com/kripken/emscripten/issues/4542, but hello.rs does seem to work when run on node via the binaryen interpreter
- This requires an up to date installation of the emscripten sdk from its incoming branch
- Unwinding is very broken
- When enabling the emscripten targets jemalloc is disabled for all targets, which results in test failures for the host

Next steps are to fix the jemalloc issue, start building the two emscripten targets on the auto builders, then start producing nightlies.

https://github.com/rust-lang/rust/issues/36317 tracks work on this.

Fixes https://github.com/rust-lang/rust/issues/36515
Fixes https://github.com/rust-lang/rust/issues/36515
Fixes https://github.com/rust-lang/rust/issues/36356

9 files changed, 13 insertions, 8 deletions

diff --git a/src/libstd/sync/barrier.rs b/src/libstd/sync/barrier.rs
index ac0f400379e..f46eab68484 100644
--- a/src/libstd/sync/barrier.rs
+++ b/src/libstd/sync/barrier.rs
@@ -118,6 +118,7 @@ mod tests {
     use thread;
 
     #[test]
+    #[cfg_attr(target_os = "emscripten", ignore)]
     fn test_barrier() {
         const N: usize = 10;
 
diff --git a/src/libstd/sync/condvar.rs b/src/libstd/sync/condvar.rs
index 3db8b05b954..a983ae716a4 100644
--- a/src/libstd/sync/condvar.rs
+++ b/src/libstd/sync/condvar.rs
@@ -270,6 +270,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(target_os = "emscripten", ignore)]
     fn notify_one() {
         let m = Arc::new(Mutex::new(()));
         let m2 = m.clone();
@@ -286,6 +287,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(target_os = "emscripten", ignore)]
     fn notify_all() {
         const N: usize = 10;
 
@@ -322,6 +324,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(target_os = "emscripten", ignore)]
     fn wait_timeout_ms() {
         let m = Arc::new(Mutex::new(()));
         let m2 = m.clone();
@@ -343,6 +346,7 @@ mod tests {
 
     #[test]
     #[should_panic]
+    #[cfg_attr(target_os = "emscripten", ignore)]
     fn two_mutexes() {
         let m = Arc::new(Mutex::new(()));
         let m2 = m.clone();
diff --git a/src/libstd/sync/mpsc/mod.rs b/src/libstd/sync/mpsc/mod.rs
index 3d9f81413dc..d9c14ef2f77 100644
--- a/src/libstd/sync/mpsc/mod.rs
+++ b/src/libstd/sync/mpsc/mod.rs
@@ -1268,7 +1268,7 @@ impl error::Error for TryRecvError {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, not(target_os = "emscripten")))]
 mod tests {
     use env;
     use super::*;
@@ -1942,7 +1942,7 @@ mod tests {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, not(target_os = "emscripten")))]
 mod sync_tests {
     use env;
     use thread;
diff --git a/src/libstd/sync/mpsc/mpsc_queue.rs b/src/libstd/sync/mpsc/mpsc_queue.rs
index d926043fbbc..8d80f942ff7 100644
--- a/src/libstd/sync/mpsc/mpsc_queue.rs
+++ b/src/libstd/sync/mpsc/mpsc_queue.rs
@@ -146,7 +146,7 @@ impl<T> Drop for Queue<T> {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, not(target_os = "emscripten")))]
 mod tests {
     use sync::mpsc::channel;
     use super::{Queue, Data, Empty, Inconsistent};
diff --git a/src/libstd/sync/mpsc/select.rs b/src/libstd/sync/mpsc/select.rs
index 51b08bd75c4..91896e1ab85 100644
--- a/src/libstd/sync/mpsc/select.rs
+++ b/src/libstd/sync/mpsc/select.rs
@@ -366,7 +366,7 @@ impl<'rx, T:Send+'rx> fmt::Debug for Handle<'rx, T> {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, not(target_os = "emscripten")))]
 #[allow(unused_imports)]
 mod tests {
     use thread;
diff --git a/src/libstd/sync/mpsc/spsc_queue.rs b/src/libstd/sync/mpsc/spsc_queue.rs
index 724d7b1be73..5858e4b6ddb 100644
--- a/src/libstd/sync/mpsc/spsc_queue.rs
+++ b/src/libstd/sync/mpsc/spsc_queue.rs
@@ -231,7 +231,7 @@ impl<T> Drop for Queue<T> {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, not(target_os = "emscripten")))]
 mod tests {
     use sync::Arc;
     use super::Queue;
diff --git a/src/libstd/sync/mutex.rs b/src/libstd/sync/mutex.rs
index 098a3e44258..812724c7a16 100644
--- a/src/libstd/sync/mutex.rs
+++ b/src/libstd/sync/mutex.rs
@@ -352,7 +352,7 @@ pub fn guard_poison<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a poison::Fla
     &guard.__lock.poison
 }
 
-#[cfg(test)]
+#[cfg(all(test, not(target_os = "emscripten")))]
 mod tests {
     use sync::mpsc::channel;
     use sync::{Arc, Mutex, Condvar};
diff --git a/src/libstd/sync/once.rs b/src/libstd/sync/once.rs
index 86d2986959c..ad9d0b37544 100644
--- a/src/libstd/sync/once.rs
+++ b/src/libstd/sync/once.rs
@@ -367,7 +367,7 @@ impl OnceState {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, not(target_os = "emscripten")))]
 mod tests {
     use panic;
     use sync::mpsc::channel;
diff --git a/src/libstd/sync/rwlock.rs b/src/libstd/sync/rwlock.rs
index 7f053c6704b..48ecae185f9 100644
--- a/src/libstd/sync/rwlock.rs
+++ b/src/libstd/sync/rwlock.rs
@@ -380,7 +380,7 @@ impl<'a, T: ?Sized> Drop for RwLockWriteGuard<'a, T> {
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, not(target_os = "emscripten")))]
 mod tests {
     #![allow(deprecated)] // rand