Fix Issue 21222 - Add windows 64 bit version of rdmd

Author: RazvanN7

script/install.sh

@@ -1197,7 +1197,7 @@ write_env_vars() {
     echo "set _OLD_D_PATH=%PATH%"
     echo "set PATH=${DUB_BIN_PATH:+$(cygpath -w "${DUB_BIN_PATH}");}${winpath};%PATH%"
     if [[ $PROCESSOR_ARCHITECTURE != x86 ]]; then
-        echo "set PATH=${winpath}64;%PATH%"
+        echo "set PATH=${winpath}64;%${winpath};PATH%"
     fi
 } > "$ROOT/$1/activate.bat"
     fi