chore: forgot linker env for raspi

Author: asimpson

build.sh

@@ -7,6 +7,7 @@ if [ "$TARGET" = "arm-unknown-linux-gnueabihf" ]
 then
   git clone --depth=1 https://github.com/raspberrypi/tools.git /tmp/tools;
   export PATH=/tmp/tools/arm-bcm2708/arm-linux-gnueabihf/bin:$PATH;
+  export CARGO_TARGET_ARM_UNKNOWN_LINUX_GNUEABIHF_LINKER=arm-linux-gnueabihf-gcc
 fi
 
 cargo build --target="$TARGET" --release