build script: added command to remove old build directories

build

@@ -205,6 +205,10 @@ else
    check_file="Makefile"
 fi
 
+# remove old build directories that were used before the unified top-level "builddir"
+# (TODO: this code be removed later)
+rm -rf ./Release ./Debug ./RelWithDebInfo ./Testing ./Build
+
 BUILD_DIR="builddir/$BUILD"
 cmake_command=(
    ${CMAKE} -B "$BUILD_DIR" -S "$ROOT_DIR" -G "$generator"