CI: run cargo doc

Link: #877 (comment)
Signed-off-by: Alyssa Ross <[email protected]>

Author: alyssais

.buildkite/main-tests.json

@@ -21,6 +21,10 @@
       "test_name": "style",
       "command": "cargo fmt --all -- --check --config format_code_in_doc_comments=true"
     },
+    {
+      "test_name": "doc",
+      "command": "RUSTDOCFLAGS=\"-D warnings\" cargo doc --workspace --all-features --no-deps"
+    },
     {
       "test_name": "unittests-gnu",
       "command": "CROSVM_USE_SYSTEM_VIRGLRENDERER=1 CROSVM_USE_SYSTEM_MINIGBM=1 cargo test --all-features --workspace",
@@ -110,4 +114,4 @@
       ]
     }
   ]
-}
+}

.buildkite/staging-tests.json

@@ -22,6 +22,10 @@
       "test_name": "staging: style",
       "command": "cd staging && cargo fmt --all -- --check --config format_code_in_doc_comments=true"
     },
+    {
+      "test_name": "staging: doc",
+      "command": "cd staging && RUSTDOCFLAGS=\"-D warnings\" cargo doc --workspace --all-features --no-deps"
+    },
     {
       "test_name": "staging: unittests-gnu",
       "command": "cd staging && cargo test --all-features --workspace",