machine: add tool to check consistency with documentation

This tool checks whether the machine package matches the documentation
in https://tinygo.org/docs/reference/machine/.

.github/workflows/linux.yml

@@ -236,6 +236,8 @@ jobs:
         run: |
           make ASSERT=1
           echo "$(pwd)/build" >> $GITHUB_PATH
+      - name: Test machine package
+        run: make check-machine
       - name: Test stdlib packages
         run: make tinygo-test
       - name: Install Xtensa toolchain