When running a 32-bit rustup on an aarch64 CPU, select a 32-bit toolc…

…hain

this mirrors a similar check that exists in rustup-init.sh

fixes rust-lang#3307

src/dist/dist.rs

@@ -346,7 +346,13 @@ impl TargetTriple {
                 (b"Linux", b"arm") => Some("arm-unknown-linux-gnueabi"),
                 (b"Linux", b"armv7l") => Some("armv7-unknown-linux-gnueabihf"),
                 (b"Linux", b"armv8l") => Some("armv7-unknown-linux-gnueabihf"),
-                (b"Linux", b"aarch64") => Some(TRIPLE_AARCH64_UNKNOWN_LINUX),
+                (b"Linux", b"aarch64") => {
+                    if cfg!(target_pointer_width = "32") {
+                        Some("armv7-unknown-linux-gnueabihf")
+                    } else {
+                        Some(TRIPLE_AARCH64_UNKNOWN_LINUX)
+                    }
+                }
                 (b"Darwin", b"x86_64") => Some("x86_64-apple-darwin"),
                 (b"Darwin", b"i686") => Some("i686-apple-darwin"),
                 (b"FreeBSD", b"x86_64") => Some("x86_64-unknown-freebsd"),