Use submodule to include the equinox.binaries

Currently the user needs to checkout two repositories side-by-side and
specify the location of it at the commandline to fully build equinox.

This includes the other repository as a submodule now to make it easier
for users/buildscripts as they can see the content of both repositories
as one linear directory structure.

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "rt.equinox.binaries"]
+	path = rt.equinox.binaries
+	url = https://github.com/eclipse-equinox/equinox.binaries.git

Jenkinsfile

@@ -12,21 +12,14 @@ pipeline {
 		jdk 'temurin-jdk17-latest'
 	}
 	stages {
-		stage('get binaries') {
-			steps{
-				dir ('rt.equinox.binaries') {
-					checkout([$class: 'GitSCM', branches: [[name: '*/master']], doGenerateSubmoduleConfigurations: false, extensions: [[$class: 'CloneOption', timeout: 120]], submoduleCfg: [], userRemoteConfigs: [[url: 'https://github.com/eclipse-equinox/equinox.binaries.git']]])
-				}
-			}
-		}
 		stage('Build') {
 			steps {
+			    sh 'git submodule update --init --recursive --remote'
 				sh """
 				mvn clean verify --batch-mode --fail-at-end -Dmaven.repo.local=$WORKSPACE/.m2/repository \
 					-Pbree-libs -Papi-check -Pjavadoc\
 					-Dcompare-version-with-baselines.skip=false \
 					-Dproject.build.sourceEncoding=UTF-8 \
-					-Drt.equinox.binaries.loc=$WORKSPACE/rt.equinox.binaries 
 				"""
 			}
 			post {

features/org.eclipse.equinox.executable.feature/pom.xml

@@ -106,6 +106,9 @@
           <name>!longnotexistingproperty</name>
         </property>
       </activation>
+      <properties>
+		  <rt.equinox.binaries.loc>${project.basedir}/../../rt.equinox.binaries</rt.equinox.binaries.loc>
+	  </properties>
       <build>
         <plugins>
           <plugin>