Allow to force non-incremental Jenkins builds

In all the builds using precompiled headers, an update to libraries will
crash the CI, as those headers will become outdated. It is then
necessary to force a full rebuild of the game by cleaning up the
workspaces.

This commit allows this CI behavior to be triggered by specifying
[CLEANBUILD] in the first line of the commit message.
This will constitute an opportunity to inform users that they need to
clean their workspaces when pulling the update.

build/jenkins/pipelines/freeBSD.Jenkinsfile

@@ -35,6 +35,16 @@ pipeline {
 		LLVM_OBJDUMP = '/usr/bin/llvm-objdump'
 	}
 	stages {
+		stage("Cleanup") {
+			when {
+				changelog '.*\\[CLEANBUILD\\].*'
+			}
+			steps {
+				script { env.CLEANBUILD = 'true' }
+				sh "git clean -fdx build/ source/"
+			}
+		}
+
 		stage ("Pre-build") {
 			steps {
 				discoverGitReferenceBuild()
@@ -70,6 +80,11 @@ pipeline {
 
 	post {
 		always {
+			script {
+				if (env.CLEANBUILD == 'true') {
+					sh "git clean -fdx build/ source/"
+				}
+			}
 			recordIssues enabledForFailure: true, qualityGates: [[threshold: 1, type: 'NEW']], tool: clang()
 		}
 	}

build/jenkins/pipelines/linux.Jenkinsfile

@@ -60,12 +60,26 @@ pipeline {
 				}
 
 				stages {
+					stage("Cleanup") {
+						when {
+							allOf {
+								environment name: 'JENKINS_PCH', value: 'pch'
+								changelog '.*\\[CLEANBUILD\\].*'
+							}
+						}
+						steps {
+							script { env.CLEANBUILD = 'true' }
+							sh "git clean -fdx build/ source/"
+						}
+					}
+
 					stage("Pre-build") {
 						steps {
 							sh "git lfs pull -I binaries/data/tests"
 							sh "git lfs pull -I \"binaries/data/mods/_test.*\""
 
 							sh "libraries/build-source-libs.sh -j1 2> ${JENKINS_COMPILER}-prebuild-errors.log"
+
 							script {
 								if (env.JENKINS_PCH == "no-pch") {
 									sh "build/workspaces/update-workspaces.sh -j1 --jenkins-tests --without-pch 2>> ${JENKINS_COMPILER}-prebuild-errors.log"
@@ -109,6 +123,16 @@ pipeline {
 						}
 					}
 				}
+
+				post {
+					always {
+						script {
+							if (env.CLEANBUILD == 'true' && env.JENKINS_PCH == 'pch') {
+								sh "git clean -fdx build/ source/"
+							}
+						}
+					}
+				}
 			}
 
 			post {

build/jenkins/pipelines/macOS.Jenkinsfile

@@ -29,6 +29,16 @@ pipeline {
 	}
 
 	stages {
+		stage("Cleanup") {
+			when {
+				changelog '.*\\[CLEANBUILD\\].*'
+			}
+			steps {
+				script { env.CLEANBUILD = 'true' }
+				sh "git clean -fdx build/ source/"
+			}
+		}
+
 		stage ("Pre-build") {
 			steps {
 				discoverGitReferenceBuild()
@@ -77,6 +87,11 @@ pipeline {
 
 	post {
 		always {
+			script {
+				if (env.CLEANBUILD == 'true') {
+					sh "git clean -fdx build/ source/"
+				}
+			}
 			recordIssues enabledForFailure: true, qualityGates: [[threshold: 1, type: 'NEW']], tool: clang()
 		}
 	}

build/jenkins/pipelines/windows.Jenkinsfile

@@ -32,6 +32,16 @@ pipeline {
 	}
 
 	stages {
+		stage("Cleanup") {
+			when {
+				changelog '.*\\[CLEANBUILD\\].*'
+			}
+			steps {
+				script { env.CLEANBUILD = 'true' }
+				bat "git clean -fdx build/ source/"
+			}
+		}
+
 		stage ("Pre-build") {
 			steps {
 				discoverGitReferenceBuild()
@@ -77,6 +87,11 @@ pipeline {
 
 	post {
 		always {
+			script {
+				if (env.CLEANBUILD == 'true') {
+					bat "git clean -fdx build/ source/"
+				}
+			}
 			recordIssues enabledForFailure: true, qualityGates: [[threshold: 1, type: 'NEW']], tool: msBuild()
 		}
 	}