fix: remove invalid rustup toolchain install for cross-compile targets

rustup toolchain install stable-<cross-target> attempts to install and
run binaries for the target platform on the build host, which fails with
"may not be able to run on this system". Cross-compilation only requires
rustup target add <target> (stdlib for the target) plus the system
cross-linker from apt. Removed the three rustup toolchain install lines.

+semver:feature

Co-authored-by: f2calv <16097639+f2calv@users.noreply.github.com>

Author: Copilot

Cargo.lock

@@ -1,7 +1,7 @@
 [package]
 name = "multi-arch-container-rust"
 authors = ["Alex Vincent <alex@far2cool.com>"]
-version = "0.1.0"
+version = "0.2.0"
 edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

Cargo.toml

@@ -10,15 +10,12 @@ if [ "$TARGETPLATFORM" = "linux/amd64" ]; then \
     echo 'TODO: need to complete and test building x86_64 FROM an arm platform??... ' ; \
     apt-get install -y g++-x86-64-linux-gnu libc6-dev-amd64-cross ; \
     rustup target add x86_64-unknown-linux-gnu ; \
-    rustup toolchain install stable-x86_64-unknown-linux-gnu ; \
 elif [ "$TARGETPLATFORM" = "linux/arm64" ]; then \
     apt-get install -y g++-aarch64-linux-gnu libc6-dev-arm64-cross ; \
     rustup target add aarch64-unknown-linux-gnu ; \
-    rustup toolchain install stable-aarch64-unknown-linux-gnu ; \
 elif [ "$TARGETPLATFORM" = "linux/arm/v7" ]; then \
     apt-get install -y g++-arm-linux-gnueabihf libc6-dev-armhf-cross ; \
     rustup target add armv7-unknown-linux-gnueabihf ; \
-    rustup toolchain install stable-armv7-unknown-linux-gnueabihf ; \
 fi
 
 
@@ -41,7 +38,7 @@ elif [ "$TARGETPLATFORM" = "linux/arm64" ]; then \
 elif [ "$TARGETPLATFORM" = "linux/arm/v7" ]; then \
     TARGET=armv7-unknown-linux-gnueabihf ; \
     export CARGO_TARGET_ARMV7_UNKNOWN_LINUX_GNUEABIHF_LINKER=arm-linux-gnueabihf-gcc ; \
-    export CC_armv7_unknown_Linux_gnueabihf=arm-linux-gnueabihf-gcc ; \
+    export CC_armv7_unknown_linux_gnueabihf=arm-linux-gnueabihf-gcc ; \
     export CXX_armv7_unknown_linux_gnueabihf=arm-linux-gnueabihf-g++ ; \
 fi \
 && cargo fetch --target $TARGET
@@ -69,7 +66,7 @@ elif [ "$TARGETPLATFORM" = "linux/arm64" ]; then \
 elif [ "$TARGETPLATFORM" = "linux/arm/v7" ]; then \
     TARGET=armv7-unknown-linux-gnueabihf ; \
     export CARGO_TARGET_ARMV7_UNKNOWN_LINUX_GNUEABIHF_LINKER=arm-linux-gnueabihf-gcc ; \
-    export CC_armv7_unknown_Linux_gnueabihf=arm-linux-gnueabihf-gcc ; \
+    export CC_armv7_unknown_linux_gnueabihf=arm-linux-gnueabihf-gcc ; \
     export CXX_armv7_unknown_linux_gnueabihf=arm-linux-gnueabihf-g++ ; \
 fi \
 && cargo build --release --target $TARGET && mv /app/target/$TARGET /app/target/final

Dockerfile

@@ -97,16 +97,8 @@ impl<T: std::fmt::Display> std::fmt::Display for DisplayOption<'_, T> {
     }
 }
 
-fn get_arch() -> String {
-    #[cfg(target_arch = "x86")]
-    let arch = String::from("x86");
-    #[cfg(target_arch = "x86_64")]
-    let arch = String::from("x86_64");
-    #[cfg(target_arch = "arm")]
-    let arch = String::from("arm");
-    #[cfg(target_arch = "aarch64")]
-    let arch = String::from("aarch64");
-    arch
+fn get_arch() -> &'static str {
+    std::env::consts::ARCH
 }
 
 fn get_app_name() -> String {