Makefile.inc1: Add new buildetc and installetc targets

These implement the steps that etcupdate (and mergemaster) need in order
to build their pristine trees, avoiding the need to use internal targets
and variables. Additionally, buildetc includes the steps needed to build
with BUILD_WITH_STRICT_TMPPATH enabled, since we need some host tools to
be available during the various build and install steps.

Reviewed by:	jhb, imp
Differential Revision:	https://reviews.freebsd.org/D41205

Makefile.inc1

@@ -1623,6 +1623,29 @@ distrib-dirs distribution: .MAKE .PHONY
 		MK_TESTS_SUPPORT=${MK_TESTS_SUPPORT} installconfig
 .endif
 
+#
+# buildetc and installetc
+#
+buildetc: .MAKE .PHONY
+	${_+_}cd ${.CURDIR}; ${MAKE} -f Makefile.inc1 _worldtmp
+	${_+_}cd ${.CURDIR}; ${MAKE} -f Makefile.inc1 _legacy
+	${_+_}cd ${.CURDIR}; ${MAKE} -f Makefile.inc1 _bootstrap-tools \
+	    MK_CROSS_COMPILER=no MK_TOOLCHAIN=no
+	${_+_}cd ${.CURDIR}; ${MAKE} -f Makefile.inc1 _obj \
+	    SUBDIR_OVERRIDE=etc
+	${_+_}cd ${.CURDIR}; ${MAKE} -f Makefile.inc1 everything \
+	    SUBDIR_OVERRIDE=etc
+
+installetc: .MAKE .PHONY
+	@echo "--------------------------------------------------------------"
+	@echo ">>> Making hierarchy"
+	@echo "--------------------------------------------------------------"
+	${_+_}cd ${.CURDIR}; ${MAKE} -f Makefile.inc1 distrib-dirs
+	@echo "--------------------------------------------------------------"
+	@echo ">>> Making distribution"
+	@echo "--------------------------------------------------------------"
+	${_+_}cd ${.CURDIR}; ${MAKE} -f Makefile.inc1 distribution
+
 #
 # buildkernel and installkernel
 #