Add SourceReferences to plugins

This allows the user to clone and checkout the source code of CDT
without knowing where the repository is. See:
https://wiki.eclipse.org/PDE/UI/SourceReferences

One use case is to right-click on a plug-in under the Plug-in dependencies in
Package Explorer view and select Import from Repository. Note that for this
EGit needs to be installed.

What this patch does is to let Tycho generate the source references in the
MANIFEST.MF of the built jars. So to test this patch, one can build the update
site locally and inspect the manifests of the (non-source) jars.

Change-Id: I807cd7842e3485ae1affcaa03ae08bdbb1677c97
Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/39549
Tested-by: Hudson CI
Reviewed-by: Alvaro Sanchez-Leon <alvsan09@gmail.com>
Tested-by: Alvaro Sanchez-Leon <alvsan09@gmail.com>

pom.xml

@@ -24,6 +24,7 @@
 		<sonar.jacoco.reportPath>${project.basedir}/../../target/jacoco.exec</sonar.jacoco.reportPath>
 		<target-platform>cdt-e4.4</target-platform>
 		<help-docs-eclipserun-repo>http://download.eclipse.org/eclipse/updates/4.4</help-docs-eclipserun-repo>
+		<tycho.scmUrl>scm:git:git://git.eclipse.org/gitroot/cdt/org.eclipse.cdt.git</tycho.scmUrl>
 	</properties>
 
 	<licenses>
@@ -550,6 +551,23 @@
 						</execution>
 					</executions>
 				</plugin>
+				<plugin>
+					<groupId>org.eclipse.tycho</groupId>
+					<artifactId>tycho-packaging-plugin</artifactId>
+					<version>${tycho-version}</version>
+					<configuration>
+						<sourceReferences>
+							<generate>true</generate>
+						</sourceReferences>
+					</configuration>
+					<dependencies>
+						<dependency>
+							<groupId>org.eclipse.tycho.extras</groupId>
+							<artifactId>tycho-sourceref-jgit</artifactId>
+							<version>${tycho-extras-version}</version>
+						</dependency>
+					</dependencies>
+				</plugin>
 				<plugin>
 					<groupId>org.apache.maven.plugins</groupId>
 					<artifactId>maven-resources-plugin</artifactId>