Move the adding of CFLAGS_LAST to bsd.sys.mk

The point of CFLAGS_LAST is to be the last thing in CFLAGS
so add it last.

For DIRDEPS_BUILD this can best be done via local.dirdeps-build.mk
which is guaranteed to be the last makefile read, but that does nothing
for non-DIRDEPS_BUILD

bsd.sys.mk is close enough to the end.

Reviewed by:	obrien
Differential Revision:	https://reviews.freebsd.org/D42001

share/mk/bsd.sys.mk

@@ -501,3 +501,8 @@ ${_tgt}: ${META_DEPS}
 .endif
 .endfor
 .endif
+
+# we are generally the last makefile read
+CFLAGS+= ${CFLAGS_LAST}
+CXXFLAGS+= ${CXXFLAGS_LAST}
+LDFLAGS+= ${LDFLAGS_LAST}

share/mk/local.autodep.mk

@@ -11,10 +11,6 @@ NOSSPPICO?= .nossppico
 PIEO?= .pieo
 OBJ_EXTENSIONS+= ${NOSSPPICO} ${PIEO}
 
-CFLAGS+= ${CFLAGS_LAST}
-CXXFLAGS+= ${CXXFLAGS_LAST}
-LDFLAGS+= ${LDFLAGS_LAST}
-
 CLEANFILES+= .depend
 
 # handy for debugging