[AIROCMLIR-597][CI] Extract Jenkinsfile helpers into helpers/*.groovy and load them in a Bootstrap stage

mlir/utils/jenkins/helpers/buildUtils.groovy

@@ -0,0 +1,57 @@
+// Build helpers: rocMLIR build, plus building/checking out CK and MIGraphX.
+// Loaded by Jenkinsfile's Bootstrap stage; consumed as buildUtils.<method>().
+// ON CHANGING THESE, ALSO CHANGE Jenkinsfile.downstream
+
+void buildProject(String target, String cmakeOpts) {
+    timeout(time: 60, activity: true, unit: 'MINUTES') {
+        cmakeBuild generator: 'Ninja',\
+            buildDir: 'build',\
+            buildType: 'RelWithDebInfo',\
+            installation: 'InSearchPath',\
+            steps: [[args: target]],\
+            cmakeArgs: """-DCMAKE_CXX_COMPILER=/opt/rocm/llvm/bin/clang++
+              -DCMAKE_C_COMPILER=/opt/rocm/llvm/bin/clang
+              ${cmakeOpts}"""
+    }
+}
+
+void buildCK(String cmakeOpts) {
+    sh '[ ! -d build ] || rm -rf build'
+    cmakeBuild generator: 'Unix Makefiles',\
+        buildDir: 'build',\
+        buildType: 'Release',\
+        installation: 'InSearchPath',\
+        cmakeArgs: """-DCMAKE_CXX_COMPILER=/opt/rocm/llvm/bin/clang++
+                      -DCMAKE_C_COMPILER=/opt/rocm/llvm/bin/clang
+                     ${cmakeOpts}
+                     """
+    sh 'cd build; make -j $(nproc)'
+}
+
+void buildMIGraphX(String cmakeOpts) {
+    sh '[ ! -d build ] || rm -rf build'
+    cmakeBuild generator: 'Unix Makefiles',\
+        buildDir: 'build',\
+        buildType: 'Release',\
+        installation: 'InSearchPath',\
+        cmakeArgs: """-DCMAKE_CXX_COMPILER=/opt/rocm/llvm/bin/clang++
+                      -DCMAKE_C_COMPILER=/opt/rocm/llvm/bin/clang
+                      -DMIGRAPHX_USE_COMPOSABLEKERNEL=OFF
+                     ${cmakeOpts}
+                     """
+    sh 'cd build; make -j $(nproc)'
+}
+
+void getAndBuildMIGraphX(String cmakeOpts) {
+    git branch: params.MIGraphXBranch, poll: false,\
+        url: 'https://github.com/ROCm/AMDMIGraphX.git'
+    buildMIGraphX(cmakeOpts)
+}
+
+void getAndBuildCK(String cmakeOpts) {
+    git branch: params.CKBranch, poll: false,\
+        url: 'https://github.com/ROCm/composable_kernel.git'
+    buildCK(cmakeOpts)
+}
+
+return this