refactor(mk): move build rules into separate scripts (#855)

See https://github.com/ooni/probe/issues/2218

MOBILE/ios/check-xcode-version

@@ -0,0 +1,19 @@
+#!/bin/bash
+
+set -euo pipefail
+
+EXPECTED_XCODE_VERSION=${EXPECTED_XCODE_VERSION:-13.4.1}
+
+printf "checking for xcodebuild... "
+command -v xcodebuild || {
+	echo "not found"
+	exit 1
+}
+
+printf "checking for Xcode version... "
+__XCODEVERSION_REAL=$(xcodebuild -version | grep ^Xcode | awk '{print $2}')
+echo $__XCODEVERSION_REAL
+[[ "$EXPECTED_XCODE_VERSION" = "$__XCODEVERSION_REAL" ]] || {
+	echo "fatal: Xcode version must be $EXPECTED_XCODE_VERSION instead of $__XCODEVERSION_REAL"
+	exit 1
+}