Move top-level AUTO_OBJ logic to Makefile.sys.inc.

Sponsored by:	Dell

Makefile.sys.inc

@@ -0,0 +1,39 @@
+# $FreeBSD$
+#
+# This is included very early from share/mk/src.sys.env.mk, after
+# /etc/src-env.conf but before /etc/make.conf, /etc/src.conf, or OBJDIR
+# handling.
+# - It is not safe to use .OBJDIR/OBJTOP/OBJROOT here.
+# - __ENV_ONLY_OPTIONS have been parsed by now except for opporutunistic
+#   MK_AUTO_OBJ.
+#
+
+.if ${MK_DIRDEPS_BUILD} == "no"
+# For AUTO_OBJ many targets do not need object directories created at top-level
+# for each visited directory.  Only when things are being built are they
+# needed.  Having AUTO_OBJ disabled in a build target is fine as it should
+# fallback to running 'make obj' as needed.  If a target is not in this list
+# then it is ran with MK_AUTO_OBJ=no in environment.
+# 'showconfig' is in the list to avoid forcing MK_AUTO_OBJ=no for it.
+AUTO_OBJ_TGT_WHITELIST+= \
+	_* all all-man build* depend everything *toolchain* includes \
+	libraries obj objlink showconfig tags xdev xdev-build native-xtools \
+	stage* create-packages* real-packages sign-packages package-pkg \
+	tinderbox universe* kernel kernels world worlds bmake
+
+# Only allow AUTO_OBJ for the whitelisted targets.  See AUTO_OBJ_TGT_WHITELIST
+# above.  MK_AUTO_OBJ not checked here for "yes" as it may not yet be enabled
+# since it is opportunistic.
+.if empty(.MAKEOVERRIDES:MMK_AUTO_OBJ)
+.for _tgt in ${AUTO_OBJ_TGT_WHITELIST}
+.if make(${_tgt})
+_CAN_USE_AUTO_OBJ?= yes
+.endif
+.endfor
+.if !defined(_CAN_USE_AUTO_OBJ)
+_MAKEARGS+=		MK_AUTO_OBJ=no
+MK_AUTO_OBJ=		no
+.endif
+.endif	# empty(.MAKEOVERRIDES:MMK_AUTO_OBJ)
+
+.endif	# ${MK_DIRDEPS_BUILD} == "no"