Expose the Freeze trait again (unstably) and forbid implementing it manually

.git-blame-ignore-revs

@@ -20,3 +20,6 @@ f97fddab91fbf290ea5b691fe355d6f915220b6e
 cc907f80b95c6ec530c5ee1b05b044a468f07eca
 # format let-chains
 b2d2184edea578109a48ec3d8decbee5948e8f35
+# test directives migration
+6e48b96692d63a79a14563f27fe5185f122434f8
+ec2cc761bc7067712ecc7734502f703fe3b024c8

.github/workflows/ci.yml

@@ -65,9 +65,20 @@ jobs:
           - name: x86_64-gnu-tools
             os: ubuntu-20.04-16core-64gb
             env: {}
+    defaults:
+      run:
+        shell: "${{ contains(matrix.os, 'windows') && 'msys2 {0}' || 'bash' }}"
     timeout-minutes: 600
     runs-on: "${{ matrix.os }}"
     steps:
+      - if: "contains(matrix.os, 'windows')"
+        uses: msys2/[email protected]
+        with:
+          msystem: "${{ contains(matrix.name, 'i686') && 'mingw32' || 'mingw64' }}"
+          update: false
+          release: true
+          path-type: inherit
+          install: "make dos2unix diffutils\n"
       - name: disable git crlf conversion
         run: git config --global core.autocrlf false
       - name: checkout the source code
@@ -461,9 +472,20 @@ jobs:
               RUST_CONFIGURE_ARGS: "--build=x86_64-pc-windows-msvc --enable-extended --enable-profiler"
               SCRIPT: python x.py dist bootstrap --include-default-paths
             os: windows-2019-8core-32gb
+    defaults:
+      run:
+        shell: "${{ contains(matrix.os, 'windows') && 'msys2 {0}' || 'bash' }}"
     timeout-minutes: 600
     runs-on: "${{ matrix.os }}"
     steps:
+      - if: "contains(matrix.os, 'windows')"
+        uses: msys2/[email protected]
+        with:
+          msystem: "${{ contains(matrix.name, 'i686') && 'mingw32' || 'mingw64' }}"
+          update: false
+          release: true
+          path-type: inherit
+          install: "make dos2unix diffutils\n"
       - name: disable git crlf conversion
         run: git config --global core.autocrlf false
       - name: checkout the source code
@@ -589,9 +611,20 @@ jobs:
             env:
               CODEGEN_BACKENDS: "llvm,cranelift"
             os: ubuntu-20.04-16core-64gb
+    defaults:
+      run:
+        shell: "${{ contains(matrix.os, 'windows') && 'msys2 {0}' || 'bash' }}"
     timeout-minutes: 600
     runs-on: "${{ matrix.os }}"
     steps:
+      - if: "contains(matrix.os, 'windows')"
+        uses: msys2/[email protected]
+        with:
+          msystem: "${{ contains(matrix.name, 'i686') && 'mingw32' || 'mingw64' }}"
+          update: false
+          release: true
+          path-type: inherit
+          install: "make dos2unix diffutils\n"
       - name: disable git crlf conversion
         run: git config --global core.autocrlf false
       - name: checkout the source code