Use Jenkins, per machine env var defined path to Qt

Use runtime discovery of cpu core count

Jenkinsfile

@@ -8,7 +8,6 @@ pipeline {
             node {
               label 'mac'
             }
-            
           }
           environment {
             QT_FATAL_WARNINGS = '1'
@@ -19,8 +18,8 @@ pipeline {
             sh 'git clean -ff -x -d .'
             sh 'git submodule update --init --recursive --force'
             sh 'rm -rf ${SHADOW_BUILD_DIR}; mkdir -p ${SHADOW_BUILD_DIR}'
-            sh 'cd ${SHADOW_BUILD_DIR}; ~/Qt/5.9.3/clang_64/bin/qmake -r ${WORKSPACE}/qgroundcontrol.pro CONFIG+=release CONFIG+=WarningsAsErrorsOn'
-            sh 'cd ${SHADOW_BUILD_DIR}; make -j24'
+            sh 'cd ${SHADOW_BUILD_DIR}; ${QT_BIN_PATH}/5.9.3/clang_64/bin/qmake -r ${WORKSPACE}/qgroundcontrol.pro CONFIG+=release CONFIG+=WarningsAsErrorsOn'
+            sh 'cd ${SHADOW_BUILD_DIR}; make -j`sysctl -n hw.ncpu`'
             sh 'ccache -s'
           }
         }