Add --runtime-id option to support cross build

When trying to cross build, Rid needs to change to the target Rid,
but architecture should use x64 as it as host.
In addition to the existing --architecture option, and additional --runtime-id option is required.

run-build.sh

@@ -90,6 +90,12 @@ while [[ $# > 0 ]]; do
             args=( "${args[@]/$2}" )
             shift
             ;;
+        --runtime-id)
+            CUSTOM_BUILD_ARGS="/p:Rid=\"$2\""
+            args=( "${args[@]/$1}" )
+            args=( "${args[@]/$2}" )
+            shift
+            ;;
         # This is here just to eat away this parameter because CI still passes this in.
         --targets)            
             args=( "${args[@]/$1}" )