add cargo clippy runs to see if it can build successfully (#143)

Author: Byron

ci/set_rust_version.bash

@@ -2,3 +2,4 @@
 set -e
 rustup default $1
 rustup target add $2
+rustup component add clippy --toolchain $1 --target $2

ci/test.bash

@@ -64,7 +64,10 @@ libz-ng-sys = { path = "./libz-ng-sys" }
 EOF
 
 set -x
+$CROSS clippy --features zlib --target $TARGET_TRIPLE
 $CROSS test --features zlib --target $TARGET_TRIPLE
 $CROSS test --features zlib-default --no-default-features --target $TARGET_TRIPLE
+$CROSS clippy --features zlib-default --no-default-features --target $TARGET_TRIPLE
 $CROSS test --features zlib-ng --no-default-features --target $TARGET_TRIPLE
+$CROSS clippy --features zlib-ng --no-default-features --target $TARGET_TRIPLE
 $CROSS test --features zlib-ng-compat --no-default-features --target $TARGET_TRIPLE