Run git clean on incremental builds

The main reason is to remove stale compiled-python files but there
is no harm in removing untracked files.
Refs #0

buildconfig/Jenkins/buildscript

@@ -107,12 +107,14 @@ fi
 # For a clean build the entire thing is removed to guarantee it is clean. All
 # other build types are assumed to be incremental and the following items
 # are removed to ensure stale build objects don't interfere with each other:
+#   - those removed by git clean -fdx --exclude=`basename $BUILD_DIR`
 #   - build/bin/**: if libraries are removed from cmake they are not deleted
 #                   from bin and can cause random failures
 #   - build/ExternalData/**: data files will change over time and removing
 #                            the links helps keep it fresh
 ###############################################################################
-BUILD_DIR=$WORKSPACE/build
+BUILD_DIR_REL=build
+BUILD_DIR=$WORKSPACE/$BUILD_DIR_REL
 if [ -z "$BUILD_DIR" ]; then
   echo "Build directory not set. Cannot continue"
   exit 1
@@ -122,6 +124,7 @@ if [[ "$CLEANBUILD" == true ]]; then
   rm -rf $BUILD_DIR
 fi
 if [ -d $BUILD_DIR ]; then
+  git clean -fdx --exclude=${BUILD_DIR_REL}
   rm -rf ${BUILD_DIR:?}/bin ${BUILD_DIR:?}/ExternalData
   find ${BUILD_DIR:?} -name 'TEST-*.xml' -delete
   if [[ -n ${CLEAN_EXTERNAL_PROJECTS} && "${CLEAN_EXTERNAL_PROJECTS}" == true ]]; then

buildconfig/Jenkins/buildscript.bat

@@ -84,12 +84,14 @@ if not "%JOB_NAME%" == "%JOB_NAME:debug=%" (
 :: For a clean build the entire thing is removed to guarantee it is clean. All
 :: other build types are assumed to be incremental and the following items
 :: are removed to ensure stale build objects don't interfere with each other:
+::   - those removed by git clean -fdx --exclude=build
 ::   - build/bin: if libraries are removed from cmake they are not deleted
 ::                   from bin and can cause random failures
 ::   - build/ExternalData/**: data files will change over time and removing
 ::                            the links helps keep it fresh
 :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
-set BUILD_DIR=%WORKSPACE%\build
+set BUILD_DIR_REL=build
+set BUILD_DIR=%WORKSPACE%\%BUILD_DIR_REL%
 call %~dp0setupcompiler.bat %BUILD_DIR%
 
 if "!CLEANBUILD!" == "yes" (
@@ -98,6 +100,7 @@ if "!CLEANBUILD!" == "yes" (
 )
 
 if EXIST %BUILD_DIR% (
+  git clean -fdx --exclude=%BUILD_DIR_REL%
   rmdir /S /Q %BUILD_DIR%\bin %BUILD_DIR%\ExternalData
   for /f %%F in ('dir /b /a-d /S "TEST-*.xml"') do del /Q %%F >/nul
   if "!CLEAN_EXTERNAL_PROJECTS!" == "true" (