Fix cross-compiling with cross-rs (nushell#9972)

I cross-compiled Nushell (from x64 to ARM64) for the first time in a
while and noticed that our [`cross-rs`](https://github.com/cross-rs)
setup was no longer working. I've fixed that by following [the latest
`cross-rs`
docs](https://github.com/cross-rs/cross/wiki/Recipes#openssl).

Cross.toml

@@ -1,9 +1,18 @@
 # Configuration for cross-rs: https://github.com/cross-rs/cross
 # Run cross-rs like this:
-# cross build --target aarch64-unknown-linux-musl --release
+# cross build --target aarch64-unknown-linux-gnu --release
+# or
+# cross build --target aarch64-unknown-linux-musl --release --features=static-link-openssl
 
 [target.aarch64-unknown-linux-gnu]
-dockerfile = "./docker/cross-rs/aarch64-unknown-linux-gnu.dockerfile"
+pre-build = [
+    "dpkg --add-architecture $CROSS_DEB_ARCH",
+    "apt-get update && apt-get install --assume-yes libssl-dev:$CROSS_DEB_ARCH clang"
+]
 
+#  NOTE: for musl you will need to build with --features=static-link-openssl
 [target.aarch64-unknown-linux-musl]
-dockerfile = "./docker/cross-rs/aarch64-unknown-linux-musl.dockerfile"
+pre-build = [
+    "dpkg --add-architecture $CROSS_DEB_ARCH",
+    "apt-get update && apt-get install --assume-yes clang"
+]