Two Lucet-related fixes to stack overflow handling.

Lucet uses stack probes rather than explicit stack limit checks as
Wasmtime does. In bytecodealliance/lucet#616, I have discovered that I
previously was not running some Lucet runtime tests with the new
backend, so was missing some test failures due to missing pieces in the
new backend.

This PR adds (i) calls to probestack, when enabled, in the prologue of
every function with a stack frame larger than one page (configurable via
flags); and (ii) trap metadata for every instruction on x86-64 that can
access the stack, hence be the first point at which a stack overflow is
detected when the stack pointer is decremented.

.github/workflows/main.yml

@@ -60,7 +60,10 @@ jobs:
     # nightly-only feature right now.
     - uses: ./.github/actions/install-rust
       with:
-        toolchain: nightly
+        # TODO (rust-lang/rust#79661): We are seeing an internal compiler error when
+        # building with the latest (2020-12-06) nightly; pin on a slightly older
+        # version for now.
+        toolchain: nightly-2020-11-29
     - run: cargo doc --no-deps --all --exclude wasmtime-cli --exclude test-programs --exclude cranelift-codegen-meta
     - run: cargo doc --package cranelift-codegen-meta --document-private-items
     - uses: actions/upload-artifact@v1
@@ -145,7 +148,7 @@ jobs:
     # flags to rustc.
     - uses: ./.github/actions/install-rust
       with:
-        toolchain: nightly
+        toolchain: nightly-2020-11-29
     - run: cargo install cargo-fuzz --vers "^0.8"
     - run: cargo fetch
       working-directory: ./fuzz
@@ -202,7 +205,7 @@ jobs:
             rust: beta
           - build: nightly
             os: ubuntu-latest
-            rust: nightly
+            rust: nightly-2020-11-29
           - build: macos
             os: macos-latest
             rust: stable
@@ -292,7 +295,7 @@ jobs:
         submodules: true
     - uses: ./.github/actions/install-rust
       with:
-        toolchain: nightly
+        toolchain: nightly-2020-11-29
     - uses: ./.github/actions/define-llvm-env
 
     # Install wasm32 targets in order to build various tests throughout the
@@ -303,7 +306,7 @@ jobs:
     # Run the x64 CI script.
     - run: ./ci/run-experimental-x64-ci.sh
       env:
-        CARGO_VERSION: "+nightly"
+        CARGO_VERSION: "+nightly-2020-11-29"
         RUST_BACKTRACE: 1
 
   # Build and test the wasi-nn module.