MFC r266566:

MFC r266566:

  Add .../share/mk to the default system make path. This will fix the problem
  with broken in-tree builds (which are used far more pervasively than I'd
  known outside the tree). However, weird results may now happen if at any
  point in the tree above you there happens to be a directory that has
  subdirectory of share/mk, as unpredictable results will follow. This was
  considered the lessor of the two evils, at least for now. In the future this
  will be removed again when the underlying issues are resolved.

  For MFCing, this is to ensure that when upgrading to head the share/mk
  in-tree is always used.  Otherwise several build features will not work.
  This passes a build using head's bmake which has this as the default
  already.

Relnotes:	yes

git-svn-id: svn://svn.freebsd.org/base/stable/10@292225 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f