disable big-endian CI test

Merlin's src/lib.rs contains hard-failure for big-endian targets because
I didn't test on them.  The test was added to the CI, but the
hard-failure wasn't removed, and cross now gives a linker error.  So
disable it entirely for now, and continue with the status quo (no
big-endian support).

.github/workflows/main.yml

@@ -31,34 +31,35 @@ jobs:
         with:
           command: test
 
-  cross-linux-test:
-    runs-on: ubuntu-latest
-    strategy:
-      fail-fast: false
-      matrix:
-        rust_target:
-          - powerpc-unknown-linux-gnu
-          - powerpc64-unknown-linux-gnu
-    timeout-minutes: 10
-    steps:
-      - uses: actions/checkout@v2
-      - name: Install Rust nightly
-        uses: actions-rs/toolchain@v1
-        with:
-            toolchain: nightly
-            profile: minimal
-            target: ${{ matrix.rust_target }}
-            default: true
-      - name: Build
-        uses: actions-rs/cargo@v1
-        with:
-          # see https://github.com/rust-embedded/cross
-          use-cross: true
-          command: build
-          args: --target ${{ matrix.rust_target }}
-      - name: Test
-        uses: actions-rs/cargo@v1
-        with:
-          use-cross: true
-          command: test
-          args: --target ${{ matrix.rust_target }} -- --test-threads=1
+  # Uncomment this when adding support for big-endian targets.
+  # cross-linux-test:
+  #   runs-on: ubuntu-latest
+  #   strategy:
+  #     fail-fast: false
+  #     matrix:
+  #       rust_target:
+  #         - powerpc-unknown-linux-gnu
+  #         - powerpc64-unknown-linux-gnu
+  #   timeout-minutes: 10
+  #   steps:
+  #     - uses: actions/checkout@v2
+  #     - name: Install Rust nightly
+  #       uses: actions-rs/toolchain@v1
+  #       with:
+  #           toolchain: nightly
+  #           profile: minimal
+  #           target: ${{ matrix.rust_target }}
+  #           default: true
+  #     - name: Build
+  #       uses: actions-rs/cargo@v1
+  #       with:
+  #         # see https://github.com/rust-embedded/cross
+  #         use-cross: true
+  #         command: build
+  #         args: --target ${{ matrix.rust_target }}
+  #     - name: Test
+  #       uses: actions-rs/cargo@v1
+  #       with:
+  #         use-cross: true
+  #         command: test
+  #         args: --target ${{ matrix.rust_target }} -- --test-threads=1