Pass debugging arguments to emcc

[tlively]

Tells emcc to enable assertions and debugging information for
wasm32-experimental-emscripten. This makes the codegen issues caused by
LLVM bug 33824 manifest more frequently at runtime and improves the wasm
debugging experience.

[rust-highfive]

r? @eddyb

(rust_highfive has picked a reviewer for you, use r? to override)

[tlively]

r? @alexcrichton

[alexcrichton]

@bors: r+

[bors]

📌 Commit 6a3e322 has been approved by alexcrichton

[bors]

⌛ Testing commit 6a3e322 with merge 8856e751e67b6301c2ad5bb2f7f8f6af80baa54a...

[bors]

💔 Test failed - status-travis

[aidanhs]

[ERROR] >> Build failed in step 'Retrieving needed toolchain components' tarballs'
[00:06:10] [04:41] / [ERROR] >> called in step '(top-level)'
[00:06:10] [04:41] / [ERROR] >>
[00:06:10] [04:41] / [ERROR] >> Error happened in: do_isl_get[scripts/build/companion_libs/121-isl.sh@741]
[00:06:10] [04:41] / [ERROR] >> called from: do_companion_libs_get[scripts/build/companion_libs.sh@15]
[00:06:10] [04:41] / [ERROR] >> called from: main[scripts/crosstool-NG.sh@591]

Hmm, not sure about this one. Sounds like a failure while downloading something? So

@bors retry

[bors]

⌛ Testing commit 6a3e322 with merge 969dd6ac0b7e66f7670005e3035ff5fff3146586...

[bors]

💔 Test failed - status-appveyor

[alexcrichton]

@bors: retry

• spurious segfault Spurious access violation on Windows #33434

[bors]

⌛ Testing commit 6a3e322 with merge e49a948...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing e49a948 to master...