ci/kokoro: add a no-default-features build

To help find missing feature cfg checks, add a build with all features
disabled to the CI scripts.

BUG=None
TEST=tools/presubmit

Change-Id: I98f38ecc3bf90cbeb081a1fafe4f2f540e4fc348
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3437362
Reviewed-by: Dennis Kempin <denniskempin@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>

ci/kokoro/build-x86_64.sh

@@ -8,5 +8,6 @@ source "$(dirname $0)/common.sh"
     ./tools/run_tests --target=host -v \
     && ./tools/clippy \
     && ./tools/fmt --check \
+    && cargo build --verbose --no-default-features \
     && mdbook build ./docs/book \
     && ./tools/cargo-doc"

tools/presubmit

@@ -83,6 +83,7 @@ aarch64_wrapper() {
 
 commands=(
     "./tools/fmt --check && ./tools/clippy"
+    "cargo build --verbose --no-default-features"
     "./tools/run_tests --target=host"
 )