Ignore missing classes

If we do not do this, we get a class loading error if we add a new
class to a public interface. This is because japicmp tries to
load the class in the old classpath as well for comparison.

subprojects/distributions/src/integTest/groovy/org/gradle/BinaryBreakageIntegrationTest.groovy

@@ -118,6 +118,7 @@ class BinaryBreakageIntegrationTest extends AbstractIntegrationSpec{
         options.classPathMode = JarArchiveComparatorOptions.ClassPathMode.TWO_SEPARATE_CLASSPATHS
         options.newClassPath = currentJars.external*.absolutePath as List
         options.oldClassPath = oldJars.external*.absolutePath as List
+        options.ignoreMissingClasses.ignoreAllMissingClasses = true
 
         def oldGradleJars = oldJars.internal.collect { new JApiCmpArchive(it, previous.version.version) }
         def currentGradleJars = currentJars.internal.collect { new JApiCmpArchive(it, buildContext.version.version) }