Add failure mode to Jenkins pipeline

.ci/Jenkinsfile

@@ -48,6 +48,8 @@ def saveArtifacts() {
 	archiveArtifacts artifacts: "${env.JOB_BASE_NAME}-*"
 }
 
+def anySuccess = false
+
 pipeline {
 	agent any
 
@@ -69,6 +71,10 @@ pipeline {
 						windowsBuild()
 						saveArtifacts()
 					}
+
+					script {
+						anySuccess = true
+					}
 				}
 			}
 		}
@@ -81,20 +87,23 @@ pipeline {
 						unixBuild()
 						saveArtifacts()
 					}
+
+					script {
+						anySuccess = true
+					}
 				}
 			}
 		}
 
-		/* If we're on the main jobs, trigger each of the downstream jobs. */
-		stage('Trigger downstream jobs') {
-			when {
-				expression {
-					return env.JOB_BASE_NAME == '86Box-TestBuildPleaseIgnore';
-				}
-			}
-
+		/* This stage has two tasks:
+		   - Fail the build if all build stages failed
+		   - Trigger downstream jobs if we're on the main job
+		   This could be done with two stages and when{} blocks, but then they
+		   would show up separately in the UI (unless JENKINS-44094 happens). */
+		stage('Finish build') {
 			steps {
 				script {
+					if (env.JOB_BASE_NAME == '86Box-TestBuildPleaseIgnore') {
 						["${env.JOB_BASE_NAME}2"].each {
 							try {
 								/* Set next build number for this job. */
@@ -115,6 +124,12 @@ pipeline {
 							      ]
 						}
 					}
+
+					if (!anySuccess) {
+						println "[!] Failing build because all build stages failed"
+						currentBuild.result = 'FAILURE'
+					}
+				}
 			}
 		}
 	}