The time is not yet ripe to break the lack of dependencies between
src/sys and the rest of the tree for builds.
o eliminate including bsd.mkopts.mk for the moment in kern.opts.mk
o No need to include src.opts.mk at all anymore. The reasons for it
  are now coverted in sys.mk and src.sys.mk.
Move inclusion of /etc/make.conf and others to old location (this also
moves local.sys.mk). The new location broke adding things to CXXFLAGS
in /etc/src.conf with +=. Move it back until that's sorted out...
Correct a typo.

MFC after:	1 week