Index: Makefile.inc1
===================================================================
--- Makefile.inc1
+++ Makefile.inc1
@@ -980,6 +980,8 @@
 		rm -f ${OBJTOP}/usr.sbin/wpa/*/.depend*; \
 	fi
 
+	sh ${.CURDIR}/tools/build/clean_deps.sh ${OBJTOP}
+
 _worldtmp: .PHONY
 	@echo
 	@echo "--------------------------------------------------------------"
Index: tools/build/clean_deps.sh
===================================================================
--- /dev/null
+++ tools/build/clean_deps.sh
@@ -0,0 +1,33 @@
+#!/bin/sh
+#
+# $FreeBSD$
+#
+# Our current approach to dependency tracking cannot cope with certain source
+# tree changes, particularly with respect to removing source files and
+# replacing generated files.  This script handles these cases in an ad-hoc
+# fashion.
+
+# Allow $OBJTOP to be set on the command line or in the environment.
+if [ -n "$1" ]; then
+	OBJTOP=$1
+fi
+if [ -z "${OBJTOP}" ]; then
+	echo "clean_deps.sh <OBJTOP path>" >&2
+	exit 1
+fi
+
+check_dep()
+{
+	if ! [ -e "$OBJTOP/$1" ]; then
+		return 1
+	fi
+	grep -q "$2" "$OBJTOP/$1"
+}
+
+# 20181211 r341825 Update Clang/LLVM to 7.0.1.
+if check_dep lib/clang/libllvm/.depend.LTO_LTO.o \
+    contrib/llvm/include/llvm/Analysis/ObjectUtils.h; then
+	echo "Removing LLVM 6 dependencies and objects"
+	find $OBJTOP/lib/clang $OBJTOP/tmp/obj-tools/lib/clang \
+	    \( -name '.depend*' -o -name '*.o' \) -delete
+fi