use rustup to install Miri (rust-lang#466)

* use rustup to install Miri

* run Miri with strict provenance enforcement

Author: RalfJung

.github/workflows/main.yml

@@ -239,6 +239,9 @@ jobs:
     - uses: actions/checkout@v1
       with:
         submodules: true
-    - name: Install Rust
-      run: ./ci/miri-rustup.sh
-    - run: MIRIFLAGS="-Zmiri-disable-isolation" cargo miri test
+    - name: Install Miri
+      run: |
+        rustup toolchain install nightly --component miri
+        rustup override set nightly
+        cargo miri setup
+    - run: MIRIFLAGS="-Zmiri-disable-isolation -Zmiri-strict-provenance" cargo miri test